Algebraic Expressions

ICSE Class 8 Mathematics · Selina Solutions Concise Mathematics Class 8 ICSE · 150 solved questions

Exercise
1(i)Exercise 11(A)

The sum of a - b + ab, b - c + bc and c - a + ca is:

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The sum of a - b + ab, b - c + bc and c - a + ca is,

= a - b + ab + b - c + bc + c - a + ca

= (a - a) + (- b + b) + ab + bc + ca.

= ab + bc + ca

Hence, option 3 is the correct option.

1(ii)Exercise 11(A)

(x3 - 5x2 + 7)+ (3x2 + 5x - 2)+ (2x3 - x + 7) is equal to:

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(x3 - 5x2 + 7) + (3x2 + 5x - 2) + (2x3 - x + 7)

= (x3 + 2x3) + (-5x2 + 3x2) + (5x - x) + (7 - 2 + 7)

= 3x3 - 2x2 + 4x + 12

Hence, option 1 is the correct option.

1(iii)Exercise 11(A)

(x3 - 5x2 + 3x + 2) - (6x2 - 4x3 + 3x + 5) is equal to:

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(x3 - 5x2 + 3x + 2) - (6x2 - 4x3 + 3x + 5)

= x3 - 5x2 + 3x + 2 - 6x2 + 4x3 - 3x - 5

= (x3 + 4x3) + (- 5x2 - 6x2) (+ 3x - 3x) + (2 - 5)

= 5x3 - 11x2 - 3

Hence, option 3 is the correct option.

1(iv)Exercise 11(A)

p - (p - q) - q - (q - p) is equal to:

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p - (p - q) - q - (q - p)

= p - p + q - q - q + p

= (p - p + p) + (q - q - q)

= p - q

Hence, option 2 is the correct option.

1(v)Exercise 11(A)

(ab - bc) - (ca - bc) + (ca - ab) is:

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(ab - bc) - (ca - bc) + (ca - ab)

= ab - bc - ca + bc + ca - ab

= (ab - ab) + (bc - bc) + (- ca + ca)

= 0

Hence, option 4 is the correct option.

2Exercise 11(A)

Separate the constants and variables from the following:

- 7, 7 + x, 7x + yz, $\sqrt{5}$, $\sqrt{xy}$, $\frac{3yz}{8}$, 4.5y - 3x, 8 - 5, 8 - 5x, 8x - 5y x p and 3y2z ÷ 4x

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Constants = -7, $\sqrt{5}$ and 8 - 5

Variables = 7 + x, 7x + yz, $\sqrt{xy}$, $\frac{3yz}{8}$, 4.5y - 3x, 8 - 5x, 8x - 5y x p and 3y2z ÷ 4x

3Exercise 11(A)

Write the number of terms in each of the following polynomials:

(i) 5x2 + 3 x ax

(ii) ax ÷ 4 - 7

(iii) ax - by + y x z

(iv) 23 + a x b ÷ 2

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(i) Terms are 5x2 and 3 x ax

Hence, number of terms = 2.

(ii) Terms are ax ÷ 4 and 7

Hence, number of terms = 2.

(iii) Terms are ax , by and y x z

Hence, number of terms = 3.

(iv) Terms are 23 and a x b ÷ 2

Hence, number of terms = 2.

4Exercise 11(A)

Separate monomials, binomials, trinomials and multinomial from the following algebraic expressions:

8 - 3x, xy2, 3y2 - 5y + 8, 9x - 3x2 + 15x3 - 7, 3x x 5y, 3x ÷ 5y, 2y ÷ 7 + 3x - 7 and 4 - ax2 + bx + y

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Monomials are those algebraic expression which consist of one term.

xy2, 3x x 5y and 3x ÷ 5y are monomials.

Binomials are those algebraic expression which consist of two terms.

8 - 3x is binomial.

Trinomials are those algebraic expression which consist of three terms.

3y2 - 5y + 8 and 2y ÷ 7 + 3x - 7 are trinomials

Multinominal are those algebraic expression which consist two or more terms.

8 - 3x, 3y2 - 5y + 8, 9x - 3x2 + 15x3 - 7, 2y ÷ 7 + 3x - 7 and 4 - ax2 + bx + y are multinomials.

5Exercise 11(A)

Write the degree of each polynomial given below:

(i) xy + 7z

(ii) x2 - 6x3 + 8

(iii) y - 6y2 + 5y8

(iv) xyz - 3

(v) xy + yz2 - zx3

(vi) x5y7 - 8x3y8 + 10x4y4z4

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(i) Degree = 2
Reason — As the polynomial contains 3 variables, we will find the sum of powers of each term.
The sum of powers of the term xy = 1 + 1 = 2
The sum of powers of the term 7z = 1
∵ Highest sum of powers = 2
∴ Degree of polynomial = 2

(ii) Degree = 3
Reason — As the polynomial contains 1 variable, degree of a polynomial is the highest power of the variable in a polynomial expression.
Highest power of polynomial = 3
∴ Degree of polynomial = 3

(iii) Degree = 8
Reason — As the polynomial contains 1 variable, degree of a polynomial is the highest power of the variable in a polynomial expression.
Highest power of polynomial = 8
∴ Degree of polynomial = 8

(iv) Degree = 3
Reason — As the polynomial contains 3 variables, we will find the sum of powers of each term.
The sum of powers of the term xyz = 1 + 1 + 1 = 3
The powers of the term 3 = 0
∵ Highest sum of powers = 3
∴ Degree of polynomial = 3

(v) Degree = 4
Reason — As the polynomial contains 3 variables, we will find the sum of powers of each term.
The sum of powers of the term xy = 1 + 1 = 2
The sum of powers of the term yz2 = 1 + 2 = 3
The sum of powers of the term zx3 = 1 + 3 = 4
∵ Highest sum of powers = 4
∴ Degree of polynomial = 4

(vi) Degree = 12
Reason — As the polynomial contains 3 variables, we will find the sum of powers of each term.
The sum of powers of the term x5y7 = 5 + 7 = 12
The sum of powers of the term - 8x3y8 = 3 + 8 = 11
The sum of powers of the term 10x4y4z4 = 4 + 4 + 4 = 12
∵ Highest sum of powers = 12
∴ Degree of polynomial = 12

6(i)Exercise 11(A)

Write the coefficient of:

ab in 7abx

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Coefficient of ab = 7x.

6(ii)Exercise 11(A)

Write the coefficient of:

7a in 7abx

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Coefficient of 7a = bx.

6(iii)Exercise 11(A)

Write the coefficient of:

5x2 in 5x2 - 5x

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Coefficient of 5x2 = 1.

6(iv)Exercise 11(A)

Write the coefficient of:

8 in a2 - 8ax + a

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Coefficient of 8 = -ax.

6(v)Exercise 11(A)

Write the coefficient of:

4xy in x2 - 4xy + y2

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Coefficient of 4xy = -1.

7(i)Exercise 11(A)

Evaluate:

-7x2 + 18x2 + 3x2 - 5x2

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-7x2 + 18x2 + 3x2 - 5x2

Arrange the polynomial with like terms together and combine them.

= (-7x2 + 18x2) + 3x2 - 5x2

= (11x2 + 3x2) - 5x2

= (14x2 - 5x2)

= 9x2

Hence, -7x2 + 18x2 + 3x2 - 5x2= 9x2

7(ii)Exercise 11(A)

Evluate:

b2y - 9b2y + 2b2y - 5b2y

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b2y - 9b2y + 2b2y - 5b2y

Arrange the polynomial with like terms together and combine them.

= (b2y - 9b2y) + 2b2y - 5b2y

= (-8b2y + 2b2y) - 5b2y

= (-6b2y - 5b2y)

= -11b2y

Hence, b2y - 9b2y + 2b2y - 5b2y = -11b2y

7(iii)Exercise 11(A)

Evaluate:

abx - 15abx - 10abx + 32abx

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abx - 15abx - 10abx + 32abx

Arrange the polynomial with like terms together and combine them.

= (abx - 15abx) - 10abx + 32abx

= (-14abx - 10abx) + 32abx

= (-24abx + 32abx)

= 8abx

Hence, abx - 15abx - 10abx + 32abx = 8abx

7(iv)Exercise 11(A)

Evaluate:

7x - 9y + 3 - 3x - 5y + 8

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7x - 9y + 3 - 3x - 5y + 8

Arrange the polynomial with like terms together and combine them.

(7x - 3x) - 9y + 3 - 5y + 8

= 4x + (- 9y - 5y) + 3 + 8

= 4x - 14y + (3 + 8)

= 4x - 14y + 11

Hence, 7x - 9y + 3 - 3x - 5y + 8 = 4x - 14y + 11

7(v)Exercise 11(A)

Evaluate:

3x2 + 5xy - 4y2 + x2 - 8xy - 5y2

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3x2 + 5xy - 4y2 + x2 - 8xy - 5y2

Arrange the polynomial with like terms together and combine them.

= (3x2 + x2) + 5xy - 4y2 - 8xy - 5y2

= 4x2 + (5xy - 8xy) - 4y2 - 5y2

= 4x2 - 3xy + (- 4y2 - 5y2)

= 4x2 - 3xy - 9y2

Hence, 3x2 + 5xy - 4y2 + x2 - 8xy - 5y2 = 4x2 - 3xy - 9y2

8(i)Exercise 11(A)

Add :

5a + 3b, a - 2b, 3a + 5b

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5a + 3b + a - 2b + 3a + 5b

Arrange the polynomial with like terms together and combine them.

= (5a + a + 3a) + (3b - 2b + 5b)

= 9a + 6b

Hence, addition of 5a + 3b, a - 2b, 3a + 5b is 9a + 6b.

8(ii)Exercise 11(A)

Add :

8x - 3y + 7z, - 4x + 5y - 4z, - x - y - 2z

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8x - 3y + 7z + (- 4x + 5y - 4z )+ (- x - y - 2z)

= 8x - 3y + 7z - 4x + 5y - 4z - x - y - 2z

Arrange the polynomial with like terms together and combine them.

= (8x - 4x - x) + (- 3y + 5y - y) + (7z - 4z - 2z)

= 3x + y + z

Hence, the addition of 8x - 3y + 7z, - 4x + 5y - 4z, - x - y - 2z is 3x + y + z.

8(iii)Exercise 11(A)

Add :

3b - 7c + 10, 5c - 2b - 15, 15 + 12c + b

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3b - 7c + 10 + 5c - 2b - 15 + 15 + 12c + b

Arrange the polynomial with like terms together and combine them.

= (3b - 2b + b) + (-7c + 5c + 12c) + (10 - 15 + 15)

= 2b + 10c + 10

Hence, addition of 3b - 7c + 10, 5c - 2b - 15, 15 + 12c + b is 2b + 10c + 10

8(iv)Exercise 11(A)

Add :

a - 3b + 3, 2a + 5 - 3c, 6c - 15 + 6b

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a - 3b + 3 + 2a + 5 - 3c + 6c - 15 + 6b

Arrange the polynomial with like terms together and combine them.

= (a + 2a) + (- 3b + 6b) + (3 + 5 - 15) + (- 3c + 6c)

= 3a + 3b - 7 + 3c

Hence, the addition of a - 3b + 3, 2a + 5 - 3c, 6c - 15 + 6b is 3a + 3b + 3c - 7

8(v)Exercise 11(A)

Add :

13ab - 9cd - xy, 5xy, 15cd - 7ab, 6xy - 3cd

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13ab - 9cd - xy + 5xy + 15cd - 7ab + 6xy - 3cd

Arrange the polynomial with like terms together and combine them.

= (13ab - 7ab) + (-9cd + 15cd - 3cd) + (-xy + 5xy + 6xy)

= 6ab + 3cd + 10xy

Hence, the addition of 13ab - 9cd - xy, 5xy, 15cd - 7ab, 6xy - 3cd is 6ab + 3cd + 10xy.

8(vi)Exercise 11(A)

Add :

x3 - x2y + 5xy2 + y3, -x3 - 9xy2 + y3, 3x2y + 9xy2

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x3 - x2y + 5xy2 + y3 + (-x3 - 9xy2 + y3) + 3x2y + 9xy2

Arrange the polynomial with like terms together and combine them.

= (x3 - x3) + (- x2y + 3x2y) + (5xy2 - 9xy2 + 9xy2) + (y3 + y3)

= 0 + 2x2y + 5xy2 + 2y3

Hence, the addition of x3 - x2y + 5xy2 + y3, -x3 - 9xy2 + y3, 3x2y + 9xy2 is 2x2y + 5xy2 + 2y3.

9Exercise 11(A)

Find the total savings of a boy who saves ₹ (4x - 6y), ₹ (6x + 2y), ₹ (4y - x) and ₹ (y - 2x) in four consecutive weeks.

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The total savings = ₹ (4x - 6y) + ₹ (6x + 2y) + ₹ (4y - x) + ₹ (y - 2x)

= 4x - 6y + 6x + 2y + 4y - x + y - 2x

Arrange the polynomial with like terms together and combine them.

= (4x + 6x - x - 2x) + (- 6y + 2y + 4y + y)

= 7x + y

Hence, the total saving is ₹ (7x + y).

10(i)Exercise 11(A)

Subtract:

4xy2 from 3xy2

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3xy2 - 4xy2

= -xy2

Hence, 3xy2 - 4xy2 = - 1xy2

10(ii)Exercise 11(A)

Subtract:

- 2x2y + 3xy2 from 8x2y

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8x2y - (-2x2y + 3xy2)

= 8x2y + 2x2y - 3xy2

Arrange the polynomial with like terms together and combine them.

= (8x2y + 2x2y) - 3xy2

= 10x2y - 3xy2

Hence, 8x2y - (- 2x2y + 3xy2) = 10x2y - 3xy2

10(iii)Exercise 11(A)

Subtract:

3a - 5b + c + 2d from 7a - 3b + c - 2d

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7a - 3b + c - 2d - (3a - 5b + c + 2d)

= 7a - 3b + c - 2d - 3a + 5b - c - 2d

Arrange the polynomial with like terms together and combine them.

= (7a - 3a) + (- 3b + 5b) + (c - c) + (- 2d - 2d)

= 4a + 2b - 4d

Hence, 7a - 3b + c - 2d - (3a - 5b + c + 2d) = 4a + 2b - 4d.

10(iv)Exercise 11(A)

Subtract:

x3 - 4x - 1 from 3x3 - x2 + 6

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3x3 - x2 + 6 - (x3 - 4x - 1)

= 3x3 - x2 + 6 - x3 + 4x + 1

Arrange the polynomial with like terms together and combine them.

= (3x3 - x3) - x2 + 4x + (6 + 1)

= 2x3 - x2 + 4x + 7

Hence, 3x3 - x2 + 6 - (x3 - 4x - 1) = 2x3 - x2 + 4x + 7

10(v)Exercise 11(A)

Subtract:

6a + 3 from a3 - 3a2 + 4a + 1

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a3 - 3a2 + 4a + 1 - (6a + 3)

= a3 - 3a2 + 4a + 1 - 6a - 3

Arrange the polynomial with like terms together and combine them.

= a3 - 3a2 + (4a - 6a) + (1 - 3)

= a3 - 3a2 - 2a - 2

Hence, a3 - 3a2 + 4a + 1 - (6a + 3) = a3 - 3a2 - 2a - 2.

10(vi)Exercise 11(A)

Subtract:

cab - 4cad - cbd from 3abc + 5bcd - cda

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3abc + 5bcd - cda - (cab - 4cad - cbd)

= 3abc + 5bcd - cda - cab + 4cad + cbd

Arrange the polynomial with like terms together and combine them.

= (3abc - abc) + (5bcd + bcd) + (- cda + 4cda)

= 2abc + 6bcd + 3cda

Hence, 3abc + 5bcd - cda - (cab - 4cad - cbd) = 2abc + 6bcd + 3cda.

10(vii)Exercise 11(A)

Subtract:

a2 + ab + b2 from 4a2 - 3ab + 2b2

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4a2 - 3ab + 2b2 - (a2 + ab + b2)

= 4a2 - 3ab + 2b2 - a2 - ab - b2

Arrange the polynomial with like terms together and combine them.

= (4a2 - a2) + (- 3ab - ab) + (2b2 - b2)

= 3a2 - 4ab + b2

Hence, 4a2 - 3ab + 2b2 - (a2 + ab + b2) = 3a2 - 4ab + b2.

11(i)Exercise 11(A)

Take away - 3x3 + 4x2 - 5x + 6 from 3x3 - 4x2 + 5x - 6.

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3x3 - 4x2 + 5x - 6 - (- 3x3 + 4x2 - 5x + 6)

= 3x3 - 4x2 + 5x - 6 + 3x3 - 4x2 + 5x - 6

Arrange the polynomial with like terms together and combine them.

= (3x3 + 3x3) + (- 4x2 - 4x2) + (5x + 5x) + (- 6 - 6)

= 6x3 - 8x2 + 10x - 12

Hence, 3x3 - 4x2 + 5x - 6 - (- 3x3 + 4x2 - 5x + 6) = 6x3 - 8x2 + 10x - 12.

11(ii)Exercise 11(A)

Take m2 + m + 4 from -m2 + 3m + 6 and the result from m2 + m + 1.

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Difference between m2 + m + 4 and - m2 + 3m + 6

- m2 + 3m + 6 - (m2 + m + 4)

= - m2 + 3m + 6 - m2 - m - 4

Arrange the polynomial with like terms together and combine them.

= (- m2 - m2) + (3m - m) + (6 - 4)

= - 2m2 + 2m + 2

And, the difference between - 2m2 + 2m + 2 and m2 + m + 1

(m2 + m + 1) - (- 2m2 + 2m + 2)

= m2 + m + 1 + 2m2 - 2m - 2

Arrange the polynomial with like terms together and combine them.

= ( m2 + 2m2) + (m - 2m) + (1 - 2)

= 3m2 - m - 1

Hence, the result is 3m2 - m - 1.

12Exercise 11(A)

Subtract the sum of 5y2 + y - 3 and y2 - 3y + 7 from 6y2 + y - 2.

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The sum of 5y2 + y - 3 and y2 - 3y + 7

5y2 + y - 3 + (y2 - 3y + 7)

= 5y2 + y - 3 + y2 - 3y + 7

Arrange the polynomial with like terms together and combine them.

= (5y2 + y2) + (y - 3y) + (- 3 + 7)

= 6y2 - 2y + 4

The difference of 6y2 - 2y + 4 from 6y2 + y - 2

= 6y2 + y - 2 - (6y2 - 2y + 4)

= 6y2 + y - 2 - 6y2 + 2y - 4

= (6y2 - 6y2) + (y + 2y) + (- 2 - 4)

= 0 + 3y - 6

Hence, the result is 3y - 6.

13Exercise 11(A)

What must be added to x4 - x3 + x2 + x + 3 to obtain x4 + x2 - 1 ?

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Let the number Z must be added to x4 - x3 + x2 + x + 3 to obtain x4 + x2 - 1

⇒ Z + (x4 - x3 + x2 + x + 3) = (x4 + x2 - 1)

⇒ Z = (x4 + x2 - 1) - (x4 - x3 + x2 + x + 3)

⇒ Z = x4 + x2 - 1 - x4 + x3 - x2 - x - 3

Arrange the polynomial with like terms together and combine them.

⇒ Z = (x4 - x4) + x3 + (x2 - x2) - x + (- 1 - 3)

⇒ Z = 0 + x3 + 0 - x - 4

Hence, the number is x3 - x - 4.

14(i)Exercise 11(A)

How much more than 2x2 + 4xy + 2y2 is 5x2 + 10xy - y2?

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Let 5x2 + 10xy - y2 be more than 2x2 + 4xy + 2y2 by Z.

2x2 + 4xy + 2y2 + Z = 5x2 + 10xy - y2

⇒ Z = 5x2 + 10xy - y2 - (2x2 + 4xy + 2y2)

⇒ Z = 5x2 + 10xy - y2 - 2x2 - 4xy - 2y2

Arrange the polynomial with like terms together and combine them.

⇒ Z = (5x2 - 2x2) + (10xy - 4xy) + (- y2 - 2y2)

⇒ Z = 3x2 + 6xy - 3y2

Hence, the number is 3x2 + 6xy - 3y2.

14(ii)Exercise 11(A)

How much less 2a2 + 1 is than 3a2 - 6 ?

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Let 2a2 + 1 be less than 3a2 - 6 by Z.

3a2 - 6 - Z = 2a2 + 1

⇒ Z = 3a2 - 6 - (2a2 + 1)

⇒ Z = 3a2 - 6 - 2a2 - 1

Arrange the polynomial with like terms together and combine them.

⇒ Z = (3a2 - 2a2) + (- 6 - 1)

⇒ Z = a2 - 7

Hence, the number is a2 - 7.

15Exercise 11(A)

If x = 6a + 8b + 9c; y = 2b - 3a - 6c and z = c - b + 3a; find :

(i) x + y + z

(ii) x - y + z

(iii) 2x - y - 3z

(iv) 3y - 2z - 5x

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(i) If x = 6a + 8b + 9c; y = 2b - 3a - 6c and z = c - b + 3a, then

x + y + z = (6a + 8b + 9c) + (2b - 3a - 6c) + (c - b + 3a)

= 6a + 8b + 9c + 2b - 3a - 6c + c - b + 3a

Arrange the polynomial with like terms together and combine them.

= (6a - 3a + 3a) + (8b + 2b - b) + (9c - 6c + c)

= 6a + 9b + 4c

Hence, x + y + z = 6a + 9b + 4c

(ii) If x = 6a + 8b + 9c; y = 2b - 3a - 6c and z = c - b + 3a, then

x - y + z = (6a + 8b + 9c) - (2b - 3a - 6c) + (c - b + 3a)

= 6a + 8b + 9c - 2b + 3a + 6c + c - b + 3a

Arrange the polynomial with like terms together and combine them.

= (6a + 3a + 3a) + (8b - 2b - b) + (9c + 6c + c)

= 12a + 5b + 16c

Hence, x - y + z = 12a + 5b + 16c

(iii) If x = 6a + 8b + 9c; y = 2b - 3a - 6c and z = c - b + 3a, then

2x - y - 3z = 2(6a + 8b + 9c) - (2b - 3a - 6c) - 3(c - b + 3a)

= 12a + 16b + 18c - 2b + 3a + 6c - 3c + 3b - 9a

Arrange the polynomial with like terms together and combine them.

= (12a + 3a - 9a) + (16b - 2b + 3b) + (18c + 6c - 3c)

= 6a + 17b + 21c

Hence, 2x - y - 3z = 6a + 17b + 21c

(iv) If x = 6a + 8b + 9c; y = 2b - 3a - 6c and z = c - b + 3a, then

3y - 2z - 5x = 3(2b - 3a - 6c) - 2(c - b + 3a) - 5(6a + 8b + 9c)

= 6b - 9a - 18c - 2c + 2b - 6a - 30a - 40b - 45c

Arrange the polynomial with like terms together and combine them.

= (-9a - 6a - 30a) + (6b + 2b - 40b) + (-18c - 2c - 45c)

= -45a - 32b - 65c

Hence, 3y - 2z - 5x = -45a - 32b - 65c

1(i)Exercise 11(B)

(9x4 - 8x3 - 12x) x (3x) is equal to:

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(3x) $\times$ (9x4 - 8x3 - 12x)

= 3x $\times$ 9x4 - 3x $\times$ 8x3 - 3x $\times$ 12x

= 27x(4+1) - 24x(3+1) - 36x(1+1)

= 27x^5 - 24x^4 - 36x^2

Hence, option 2 is the correct option.

1(ii)Exercise 11(B)

(9x4 - 12x3 - 18x) ÷ (3x) is equal to:

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(9x4 - 12x3 - 18x) ÷ (3x)

= (9x4 ÷ 3x) - (12x3 ÷ 3x) - (18x ÷ 3x)

= 3x(4-1) - 4x(3-1) - 6x(1-1)

= 3x3 - 4x2 - 6

Hence, option 3 is the correct option.

1(iii)Exercise 11(B)

$\Big(\frac{10}{3}xy^2z\Big)$ x $\Big(-\frac{9}{5}x^2z\Big)$ is equal to:

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$$\begin{aligned}\Big(\frac{10}{3}xy^2z\Big) \times \Big(-\frac{9}{5}x^2z\Big)\\[1em] = \Big(-\frac{10 \times 9}{3 \times 5}x^{1+2}y^2z^{1+1}\Big)\\[1em] = \Big(-\frac{90}{15}x^{3}y^2z^{2}\Big)\\[1em] = (-6x^3y^2z^2)\end{aligned}$$

Hence, option 1 is the correct option.

1(iv)Exercise 11(B)

(x3 + y2) x 10x2 is equal to :

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(x3+ y2) $\times$ 10x2

= 10x2 $\times$ x3 + 10x2 $\times$ y2

= 10x(2+3) + 10x2y2

= 10x5 + 10x2y2

Hence, option 2 is the correct option.

1(v)Exercise 11(B)

(a3 - b3) ÷ (a - b) is equal to :

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(a3 - b3) ÷ (a - b)

[∵ As we know, (x3 - y3) = (x - y)(x2 + y2 + xy)]

∴ (a3 - b3) ÷ (a - b) = $\frac{(a - b)(a^2 + b^2 + ab)}{(a - b)}$

= $\frac{\cancel{(a - b)}(a^2 + b^2 + ab)}{\cancel{(a - b)}}$

= (a2 + b2 + ab)

Hence, option 1 is the correct option.

2(i)Exercise 11(B)

Multiply :

8ab2 by - 4a3b4

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8ab2 x (- 4a3b4)

= 8 x (-4) a(1+3) b(2+4)

= -32 a4 b6

Hence, 8ab2 x (- 4a3b4) = -32a4 b6

2(ii)Exercise 11(B)

Multiply :

$\frac{2}{3}$ ab by - $\frac{1}{4}$ a2b

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$$\begin{aligned}\frac{2}{3}ab \times \Big(-\frac{1}{4}a^2b\Big)\\[1em] = -\frac{2 \times 1}{3 \times 4}a^{1+2}b^{1+1}\\[1em] = -\frac{2}{12}a^3b^2\\[1em] = -\frac{1}{6}a^3b^2\end{aligned}$$

Hence, $\frac{2}{3}$ ab x (- $\frac{1}{4}$ a2b) = $-\frac{1}{6}$a3b2.

2(iii)Exercise 11(B)

Multiply :

-5cd2 by - 5cd2

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(-5cd2) x (- 5cd2)

= (-5) x (-5) c(1+1)d(2+2)

= 25c2d4

Hence, (-5cd2) x (-5cd2) = 25c2d4

2(iv)Exercise 11(B)

Multiply :

4a and 6a + 7

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4a x (6a + 7)

= 4a x 6a + 4a x 7

= 24a(1+1) + 28a

= 24a2 + 28a

Hence, 4a x (6a + 7) = 24a2 + 28a

2(v)Exercise 11(B)

Multiply :

-8x and 4 - 2x - x2

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-8x $\times$ (4 - 2x - x2)

= (-8x) $\times$ 4 - (-8x) $\times$ 2x - (-8x) $\times$ x2

= -32x + 16x(1+1) + 8x(1+2)

= -32x + 16x2 + 8x3

Hence, (-8x) x (4 - 2x - x2) = -32x + 16x2 + 8x3

2(vi)Exercise 11(B)

Multiply :

2a2 - 5a - 4 and -3a

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-3a x (2a2 - 5a - 4)

= -3a x 2a2 - (-3a) x 5a - (-3a) x 4

= -6a(2+1) + 15a(1+1) + 12a

= -6a3 + 15a2 + 12a

Hence, (2a2 - 5a - 4) x (-3a) = -6a3 + 15a2 + 12a

2(vii)Exercise 11(B)

Multiply :

x + 4 by x - 5

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(x + 4) $\times$ (x - 5)

= x $\times$ (x - 5) + 4 $\times$ (x - 5)

= x $\times$ x - x $\times$ 5 + 4 $\times$ x - 4 $\times$ 5

= x2 - 5x + 4x - 20

= x2 - x - 20

Hence, (x + 4) x (x - 5) = x2 - x - 20

2(viii)Exercise 11(B)

Multiply :

5a - 1 by 7a - 3

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(5a - 1) x (7a - 3)

= 5a x (7a - 3) - 1 x (7a - 3)

= 5a x 7a - 5a x 3 - 1 x 7a - 1 x (-3)

= 35a(1+1) - 15a - 7a + 3

= 35a2 - 22a + 3

Hence, (5a - 1) x (7a - 3) = 35a2 - 22a + 3

2(ix)Exercise 11(B)

Multiply :

12a + 5b by 7a - b

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(12a + 5b) x (7a - b)

= 12a x 7a - 12a x b + 5b x 7a - 5b x b

= 84a(1+1) - 12ab + 35ab - 5b(1+1)

= 84a2 + 23ab - 5b2

Hence, (12a + 5b) x (7a - b) = 84a2 + 23ab - 5b2

2(x)Exercise 11(B)

Multiply :

x2 + x + 1 by 1 - x

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(x2 + x + 1) $\times$ (1 - x)

= 1 $\times$ (x2 + x + 1) - x $\times$ (x2 + x + 1)

= (1 $\times$ x2 + 1 $\times$ x + 1 $\times$ 1) - (x $\times$ x2 + x $\times$ x + x $\times$ 1)

= x2 + x + 1 - (x3 + x2 + x)

= x2 + x + 1 - x3 - x2 - x

= (x2 - x2) + (x - x) + 1 - x3

= 1 - x3

Hence, (x2 + x + 1) $\times$ (1 - x) = 1 - x3

2(xi)Exercise 11(B)

Multiply :

2m2 - 3m - 1 and 4m2 - m - 1

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(2m2 - 3m - 1) x (4m2 - m - 1)

= 2m2 x 4m2 - 2m2 x m - 2m2 x 1 - 3m x 4m2 - 3m x (-m) - 3m x (-1) - 1 x 4m2 - 1 x (- m) - 1 x (-1)

= 8m(2+2) - 2m(2+1) - 2m2 - 12m(2+1) + 3m(1+1) + 3m - 4m2 + m + 1

= 8m4 - 2m3 - 2m2 - 12m3 + 3m2 + 3m - 4m2 + m + 1

= 8m4 - 2m3 - 12m3 - 2m2 + 3m2 - 4m2 + 3m + m + 1

= 8m4 - 14m3 - 3m2 + 4m + 1

Hence, (2m2 - 3m - 1) x (4m2 - m - 1) = 8m4 - 14m3 - 3m2 + 4m + 1

2(xii)Exercise 11(B)

Multiply :

a2, ab and b2

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(a2 x ab) x b2

= a(2+1)b x b2

= a3b x b2

= a3b(2+1)

= a3b3

Hence, a2 x ab x b2 = a3b3

2(xiii)Exercise 11(B)

Multiply :

abx, - 3a2x and 7b2x3

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abx $\times$ (- 3a2x) $\times$ 7b2x3

= (-3 $\times$ 7) a(1+2)b(1+2)x(1+1+3)

= -21 a3b3x5

Hence, (abx) $\times$ (- 3a2x) $\times$ (7b2x3) = -21a3b3x5

2(xiv)Exercise 11(B)

Multiply :

- 3bx, - 5xy and - 7b3y2

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-3bx $\times$ (-5xy) $\times$ (-7b3y2)

= -3 $\times$ (-5) $\times$ (-7) b(1+3)x(1+1)y(1+2)

= -105 b4x2y3

Hence, (- 3bx) $\times$ (- 5xy) $\times$ (- 7b3y2) = -105b4x2y3

2(xv)Exercise 11(B)

Multiply :

- $\frac{3}{2}$ x5y3 and $\frac{4}{9}$ a2x3y

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$$\begin{aligned}-\frac{3}{2}x^5y^3 \times \frac{4}{9}a^2x^3y\\[1em] = -\frac{3 \times 4}{2 \times 9}a^2x^{5+3}y^{3+1}\\[1em] = -\frac{12}{18}a^2x^8y^4\\[1em] = -\frac{2}{3}a^2x^8y^4\\[1em]\end{aligned}$$

Hence, - $\frac{3}{2}$ x5 y3 x $\frac{4}{9}$ a2x3y = - $\frac{2}{3}$ a2x8y4

2(xvi)Exercise 11(B)

Multiply :

$-\frac{2}{3}$ a7b2 and $-\frac{9}{4}$ ab5

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$$\begin{aligned}-\frac{2}{3}a^7b^2 \times \Big(-\frac{9}{4}ab^5\Big)\\[1em] = \frac{2 \times 9}{3 \times 4}a^{7 + 1}b^{2+5}\\[1em] = \frac{18}{12}a^8b^7\\[1em] = \frac{3}{2}a^8b^7\\[1em]\end{aligned}$$

Hence, - $\frac{2}{3}$ a7b2 x - $\frac{9}{4}$ ab5 = $\frac{3}{2}$ a8b7

2(xvii)Exercise 11(B)

Multiply :

2a3 - 3a2b and $-\frac{1}{2}$ ab2

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$$\begin{aligned}(2a^3 - 3a^2b) \times \Big(-\frac{1}{2}ab^2\Big)\\[1em] = \Big[2a^3 \times (- \frac{1}{2}ab^2) - 3a^2b \times (- \frac{1}{2}ab^2)\Big]\\[1em] = - \frac{1 \times 2}{2}a^{3+1}b^2 + \frac{1 \times 3}{2}a^{2+1}b^{1+2}\\[1em] = - \frac{2}{2}a^4b^2 + \frac{3}{2}a^3b^3\\[1em] = - a^4b^2 + \frac{3}{2}a^3b^3\\[1em]\end{aligned}$$

Hence, 2a3 - 3a2b x $-\frac{1}{2}$ ab2 = -a4b2 + $\frac{3}{2}$ a3b3

2(xviii)Exercise 11(B)

Multiply :

2x + $\frac{1}{2}$ y and 2x - $\frac{1}{2}$ y

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$$\begin{aligned}\Big(2x + \frac{1}{2}y\Big) \times \Big(2x - \frac{1}{2}y\Big)\\[1em] = 2x \times \Big(2x - \frac{1}{2}y\Big) + \frac{1}{2}y \times \Big(2x - \frac{1}{2}y\Big)\\[1em] =\Big(2x \times 2x - 2x \times \frac{1}{2}y\Big) + \Big(\frac{1}{2}y \times 2x - \frac{1}{2}y \times \frac{1}{2}y\Big)\\[1em] =\Big(4x^{1+1} - \frac{2xy}{2}\Big) + \Big(\frac{2xy}{2} - \frac{1 \times 1}{2 \times 2}y^{1+1}\Big)\\[1em] = (4x^2 - xy) + \Big(xy - \frac{1}{4}y^{2}\Big)\\[1em] = 4x^2 - xy + xy - \frac{1}{4}y^{2}\\[1em] = 4x^2 - \cancel{xy} + \cancel{xy} - \frac{1}{4}y^{2}\\[1em] = 4x^2 - \frac{1}{4}y^2\end{aligned}$$

Hence, 2x + $\frac{1}{2}$ y x 2x - $\frac{1}{2}$ y = 4x2 - $\frac{1}{4}$ y2

3(i)Exercise 11(B)

Multiply :

5x2 - 8xy + 6y2 - 3 by - 3xy

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(5x2 - 8xy + 6y2 - 3) $\times$ (- 3xy)

= 5x2 $\times$ (- 3xy) - 8xy $\times$ (- 3xy) + 6y2 $\times$ (- 3xy) - 3 $\times$ (- 3xy)

= -15x(2+1)y + 24x(1+1)y(1+1) - 18xy(2+1) + 9xy

= -15x3y + 24x2y2 - 18xy3 + 9xy

Hence, (5x2 - 8xy + 6y2 - 3) x (- 3xy) = -15x3y + 24x2y2 - 18xy3 + 9xy

3(ii)Exercise 11(B)

Multiply :

3 - $\frac{2}{3}$ xy + $\frac{5}{7}$ xy2 - $\frac{16}{21}$ x2y by - 21x2y2

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$$\begin{aligned}\Big(3 - \frac{2}{3}xy + \frac{5}{7}xy^2 - \frac{16}{21}x^2y\Big) \times (-21x^2y^2)\\[1em] = \Big(3 \times (-21x^2y^2) - \frac{2}{3}xy \times (-21x^2y^2) + \frac{5}{7}xy^2 \times (-21x^2y^2) - \frac{16}{21}x^2y \times (-21x^2y^2)\Big)\\[1em] = \Big(-63x^2y^2 - \frac{2 \times (-21)}{3}x^{1+2}y^{1+2} + \frac{5\times (-21)}{7}x^{1+2}y^{2+2} - \frac{16 \times (-21)}{21}x^{2+2}y^{1+2}\Big)\\[1em] = -63x^2y^2 - \frac{-42}{3}x^3y^3 + \frac{-105}{7}x^3y^4 + \frac{16 \times \cancel{(21)}}{\cancel{21}}x^4y^3\\[1em] = -63x^2y^2 + 14x^3y^3 - 15x^3y^4 + 16x^4y^3\end{aligned}$$

Hence, (3 - $\frac{2}{3} xy + \frac{5}{7} xy^2 - \frac{16}{21}$ x2y) x (- 21x2y2) = -63x2y2 + 14x3y3 - 15x3y4 + 16x4y3

3(iii)Exercise 11(B)

Multiply :

6x3 - 5x + 10 by 4 - 3x2

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(6x3 - 5x + 10) $\times$ (4 - 3x2)

= 4 $\times$ (6x3 - 5x + 10) - 3x2 $\times$ (6x3 - 5x + 10)

= 24x3 - 20x + 40 - 18x(3+2) + 15x(1+2) - 30x2

= 24x3 - 20x + 40 - 18x5 + 15x3 - 30x2

= - 18x5 + 24x3 + 15x3 - 30x2 - 20x + 40

= - 18x5 + 39x3 - 30x2 - 20x + 40

Hence, (6x3 - 5x + 10) x (4 - 3x2) = - 18x5 + 39x3 - 30x2 - 20x + 40

3(iv)Exercise 11(B)

Multiply :

2y - 4y3 + 6y5 by y2 + y - 3

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(2y - 4y3 + 6y5) x (y2 + y - 3)

= 2y x (y2 + y - 3) - 4y3 x (y2 + y - 3) + 6y5 x (y2 + y - 3)

= 2y(1+2) + 2y(1+1) - 6y - 4y(3+2) - 4y(3+1) + 12y3 + 6y(5+2) + 6y(5+1) - 18y5

= 2y3 + 2y2 - 6y - 4y5 - 4y4 + 12y3 + 6y7 + 6y6 - 18y5

= 6y7 + 6y6 - 18y5 - 4y5 - 4y4 + 12y3 + 2y3 + 2y2 - 6y

= 6y7 + 6y6 - 22y5 - 4y4 + 14y3 + 2y2 - 6y

Hence, (2y - 4y3 + 6y5) x (y2 + y - 3) = 6y7 + 6y6 - 22y5 - 4y4 + 14y3 + 2y2 - 6y

3(v)Exercise 11(B)

Multiply :

5p2 + 25pq + 4q2 by 2p2 - 2pq + 3q2

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(5p2 + 25pq + 4q2) x (2p2 - 2pq + 3q2)

= 5p2 x (2p2 - 2pq + 3q2) + 25pq x (2p2 - 2pq + 3q2) + 4q2 x (2p2 - 2pq + 3q2)

= 10p(2+2) - 10p(2+1)q + 15p2q2 + 50p(1+2)q - 50p(1+1)q(1+1) + 75pq(1+2) + 8p2q2 - 8pq(2+1) + 12q(2+2)

= 10p4 - 10p3q + 15p2q2 + 50p3q - 50p2q2 + 75pq3 + 8p2q2 - 8pq3 + 12q4

= 10p4 - 10p3q + 50p3q + 15p2q2 - 50p2q2 + 8p2q2 + 75pq3 - 8pq3 + 12q4

= 10p4 + 40p3q - 27p2q2 + 67pq3 + 12q4

Hence, (5p2 + 25pq + 4q2) x (2p2 - 2pq + 3q2) = 10p4 + 40p3q - 27p2q2 + 67pq3 + 12q4

4(i)Exercise 11(B)

Simplify:

(7x - 8) (3x + 2)

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(7x - 8) (3x + 2)

= 7x (3x + 2) - 8 (3x + 2)

= 21x(1+1) + 14x - 24x - 16

= 21x2 + 14x - 24x - 16

= 21x2 - 10x - 16

Hence, (7x - 8) (3x + 2) = 21x2 - 10x - 16

4(ii)Exercise 11(B)

Simplify:

(px - q) (px + q)

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(px - q) (px + q)

= px (px + q) - q (px + q)

= p(1+1)x(1+1) + pqx - pqx - q(1+1)

= p2x2 + pqx - pqx - q2

= p2x2 - q2

Hence, (px - q) (px + q) = p2x2 - q2

4(iii)Exercise 11(B)

Simplify:

(5a + 5b - c) (2b - 3c)

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(5a + 5b - c) (2b - 3c)

= 5a (2b - 3c) + 5b (2b - 3c) - c (2b - 3c)

= 10ab - 15ac + 10b(1+1) - 15bc - 2bc + 3c(1+1)

= 10ab - 15ac + 10b2 - 17bc + 3c2

Hence, (5a + 5b - c) (2b - 3c) = 10ab - 15ac + 10b2 - 17bc + 3c2

4(iv)Exercise 11(B)

Simplify:

(4x - 5y) (5x - 4y)

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(4x - 5y) (5x - 4y)

= 4x (5x - 4y) - 5y (5x - 4y)

= 20x(1+1) - 16xy - 25xy + 20y(1+1)

= 20x2 - 41xy + 20y2

Hence, (4x - 5y) (5x - 4y) = 20x2 - 41xy + 20y2

4(v)Exercise 11(B)

Simplify:

(3y + 4z) (3y - 4z) + (2y + 7z) (y + z)

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(3y + 4z) (3y - 4z) + (2y + 7z) (y + z)

= [3y(3y - 4z) + 4z(3y - 4z)] + [2y (y + z) + 7z (y + z)]

= [9y2 - 12yz + 12yz - 16z2] + [2y2 + 2yz + 7zy + 7z2]

= 9y2 - 16z2 + 2y2 + 9zy + 7z2

= 9y2 + 2y2 + 9zy - 16z2 + 7z2

= 11y2 + 9yz - 9z2

Hence, (3y + 4z) (3y - 4z) + (2y + 7z) (y + z) = 11y2 + 9yz - 9z2

5Exercise 11(B)

The adjacent sides of a rectangle are x2 - 4xy + 7y2 and x3 - 5xy2. Find its area.

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Given:

Dimensions of the rectangle = x2 - 4xy + 7y2 and x3 - 5xy2

As we know, area of rectangle = l x b

So, putting the value

(x2 - 4xy + 7y2) $\times$ (x3 - 5xy2)

= x2 $\times$ (x3 - 5xy2) - 4xy $\times$ (x3 - 5xy2) + 7y2 $\times$ (x3 - 5xy2)

= x(2+3) - 5x(2+1)y2 - 4x(1+3)y + 20x(1+1)y(1+2) + 7x3y2 - 35xy(2+2)

= x5 - 5x3y2 + 7x3y2 - 4x4y + 20x2y3 - 35xy4

= x5 + 2x3y2 - 4x4y + 20x2y3 - 35xy4

Hence, the area of the rectangle = x5 + 2x3y2 - 4x4y + 20x2y3 - 35xy4

6Exercise 11(B)

The base and the altitude of a triangle are (3x - 4y) and (6x + 5y) respectively. Find its area.

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Given:

Base of a triangle = (3x - 4y)

Altitude of a triangle = (6x + 5y)

As we know that the area of triangle = $\frac{1}{2}$ x base x altitude

$$\begin{aligned}\frac{1}{2} \times (3x - 4y) \times (6x + 5y)\\[1em] = \frac{1}{2} \times (3x (6x + 5y) - 4y (6x + 5y))\\[1em] = \frac{1}{2} \times (18x^2 + 15xy - 24xy - 20y^2)\\[1em] = \frac{1}{2} \times (18x^2 - 9xy - 20y^2)\end{aligned}$$

Hence, the area of tirangle = $\frac{1}{2}$ (18x2 - 9xy - 20y2) sq. unit

7Exercise 11(B)

Multiply - 4xy3 and 6x2y and verify your result for x = 2 and y = 1.

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(- 4xy3) $\times$ (6x2y)

= - 24x(1+2)y(3+1)

= - 24x3y4

Hence, (- 4xy3) $\times$ (6x2y) = - 24x3y4

Putting x = 2 and y = 1

Taking LHS:

(- 4xy3) x (6x2y)

= (- 4 x 2 x 13) x (6 x 22 x 1)

= (- 4 x 2 x 1) x (6 x 4 x 1)

= (- 8) x (24)

= - 192

Taking RHS:

- 24x3y4

= - 24 x 23 x 14

= - 24 x 8 x 1

= - 192

Hence, LHS = RHS

So, (- 4xy3) $\times$ (6x2y) = - 24x3y4

8Exercise 11(B)

Find the value of (3x3) x (-5xy2) x (2x2yz3) for x = 1, y = 2 and z = 3.

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(3x3) $\times$ (-5xy2) $\times$ (2x2yz3)

= (- 15x(3+1)y2) $\times$ (2x2yz3)

= (- 15x4y2) $\times$ (2x2yz3)

= - 30x(4+2)y(2+1)z3

= - 30x6y3z3

Putting the value x = 1, y = 2 and z = 3, we get

- 30 x 16 x 23 x 33

= - 30 x 1 x 8 x 27

= - 6480

Hence, the value of (3x3) x (-5xy2) x (2x2yz3) for x = 1, y = 2 and z = 3 is - 6480

9Exercise 11(B)

Evaluate (3x4y2) (2x2y3) for x = 1 and y = 2.

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(3x4y2) $\times$ (2x2y3)

= 6x(4+2)y(2+3)

= 6x6y5

Putting x = 1 and y = 2, we get

6 x 16 x 25

= 6 x 1 x 32

= 192

Hence, (3x4y2) (2x2y3) for x = 1 and y = 2 is 192

10Exercise 11(B)

Evaluate (x5) x (3x2) x (-2x) for x = 1.

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Given:

(x5) $\times$ (3x2) $\times$ (-2x)

= 3x(5+2) $\times$ (-2x)

= 3x7 $\times$ (-2x)

= - 6x(7+1)

= - 6x8

For x = 1

- 6 x 18

= - 6 x 1

= - 6

Hence, the value of (x5) $\times$ (3x2) x (-2x) for x = 1 is -6

11(i)Exercise 11(B)

Divide:

- 70a3 by 14a2

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- 70a3 ÷ 14a2

= - $\frac{70}{14}$ a(3-2)

= - 5 a1

Hence, - 70a3 ÷ 14a2 = - 5 a

11(ii)Exercise 11(B)

Divide:

24x3y3 by - 8y2

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(24x3y3) ÷ (- 8y2)

= - $\frac{24}{8}$ x3y(3-2)

= - 3 x3y1

Hence, (24x3y3) ÷ (- 8y2) = - 3 x3y

11(iii)Exercise 11(B)

Divide:

15a4b by - 5a3b

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(15a4b) ÷ (- 5a3b)

= - $\frac{15}{5}$ a(4-3)b(1-1)

= - 3a1b0

Hence, (15a4b) ÷ (- 5a3b) = - 3a

11(iv)Exercise 11(B)

Divide:

- 24x4d3 by - 2x2d5

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(- 24x4d3) ÷ (- 2x2d5)

= $\frac{24}{2}$ x(4-2)d(3-5)

= 12 x2d(-2)

= $\frac{12x^2}{d^2}$

Hence, (- 24x4d3) ÷ (- 2x2d5) = $\frac{12x^2}{d^2}$

11(v)Exercise 11(B)

Divide:

63a4b5c6 by - 9a2b4c3

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(63a4b5c6) ÷ (- 9a2b4c3)

= - $\frac{63}{9}$ a(4-2)b(5-4)c(6-3)

= - 7a2b1c3

Hence, (63a4b5c6) ÷ (- 9a2b4c3) = - 7a2bc3

11(vi)Exercise 11(B)

Divide:

8x - 10y + 6c by 2

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(8x - 10y + 6c) ÷ 2

= (8x ÷ 2) - (10y ÷ 2) + (6c ÷ 2)

= 4x - 5y + 3c

Hence, (8x - 10y + 6c) ÷ 2 = 4x - 5y + 3c

11(vii)Exercise 11(B)

Divide:

15a3b4 - 10a4b3 - 25a3b6 by -5a3b2

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(15a3b4 - 10a4b3 - 25a3b6) ÷ (-5a3b2)

= (15a3b4 ÷ (- 5a3b2)) - (10a4b3 ÷ (- 5a3b2)) - (25a3b6 ÷ (- 5a3b2))

= $\Big($- $\frac{15}{5}$ a(3-3)b(4-2)$\Big)$ - $\Big($- $\frac{10}{5}$ a(4-3)b(3-2)$\Big)$ - $\Big($- $\frac{25}{5}$ a(3-3)b(6-2)$\Big)$

= - 3 a0b2 + 2 a1b1 + 5 a0b4

= - 3b2 + 2 ab + 5b4

Hence, (15a3b4 - 10a4b3 - 25a3b6) ÷ (- 5a3b2) = - 3b2 + 2 ab + 5b4

11(viii)Exercise 11(B)

Divide:

- 14x6y3 - 21x4y5 + 7x5y4 by 7x2y2

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(- 14x6y3 - 21x4y5 + 7x5y4) ÷ 7x2y2

= (- 14x6y3 ÷ 7x2y2) - (21x4y5 ÷ 7x2y2) + (7x5y4 ÷ 7x2y2)

= $\Big($ - $\frac{14}{7}$ x(6-2)y(3-2) $\Big)$ - $\Big($ $\frac{21}{7}$ x(4-2)y(5-2) $\Big)$ - $\Big($ - $\frac{7}{7}$ x(5-2)y(4-2) $\Big)$

= - 2 x4y1 - 3 x2y3 + 1 x3y2

Hence, (- 14x6y3 - 21x4y5 + 7x5y4) ÷ 7x2y2 = - 2 x4y - 3 x2y3 + x3y2

11(ix)Exercise 11(B)

Divide:

a2 + 7a + 12 by a + 4

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(a2 + 7a + 12) ÷ (a + 4)

= (a2 + 3a + 4a + 12) ÷ (a + 4)

= [a(a + 3) + 4(a + 3)] ÷ (a + 4)

= [(a + 3)(a + 4)] ÷ (a + 4)

= $\frac{(a + 3)\cancel{(a + 4)}}{\cancel{(a + 4)}}$

= (a + 3)

Hence, (a2 + 7a + 12) ÷ (a + 4) = a + 3

11(x)Exercise 11(B)

Divide:

x2 + 3x - 54 by x - 6

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(x2 + 3x - 54) ÷ (x - 6)

= (x2 + 9x - 6x - 54) ÷ (x - 6)

= [x(x + 9) - 6(x + 9)] ÷ (x - 6)

= [(x + 9)(x - 6)] ÷ (x - 6)

= $\frac{(x + 9)\cancel{(x - 6)}}{\cancel{(x - 6)}}$

= (x + 9)

Hence, (x2 + 3x - 54) ÷ (x - 6) = x + 9

11(xi)Exercise 11(B)

Divide:

12x2 + 7xy - 12y2 by 3x + 4y

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(12x2 + 7xy - 12y2) ÷ (3x + 4y)

= (12x2 + 16xy - 9xy - 12y2) ÷ (3x + 4y)

= [4x(3x + 4y) - 3y(3x + 4y)] ÷ (3x + 4y)

= [(3x + 4y)(4x - 3y)] ÷ (3x + 4y)

= $\frac{[\cancel{(3x + 4y)}(4x - 3y)]}{\cancel{(3x + 4y)}}$

= 4x - 3y

Hence, (12x2 + 7xy - 12y2) ÷ (3x + 4y) = (4x - 3y)

11(xii)Exercise 11(B)

Divide:

x6 - 8 by x2 - 2

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(x6 - 8) ÷ (x2 - 2)

= (x2x3 - 23) ÷ (x2 - 2)

[Using the formula (a3 - b3) = (a - b)(a2 + ab + b2)]

= [(x2 - 2)(x4 + 2x2 + 4)] ÷ (x2 - 2)

= $\frac{\cancel{(x^2 - 2)}(x^4 + 2x^2 + 4)}{\cancel{(x^2 - 2)}}$

= (x4 + 2x2 + 4)

Hence,(x6 - 8) ÷ (x2 - 2) = (x4 + 2x2 + 4)

11(xiii)Exercise 11(B)

Divide:

6x3 - 13x2 - 13x + 30 by 2x2 - x - 6

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Dividing 6x3 - 13x2 - 13x + 30 by 2x2 - x - 6

$$\begin{array}{l} \phantom{2x^2 - x - 6)}{3x - 5} \\ 2x^2 - x - 6\overline{\smash{\big)}6x^3 - 13x^2 - 13x + 30} \\ \phantom{2x^2 - x - 6}\underline{\underset{-}{}6x^3 \underset{+}{-}\phantom{0}3x^2 \underset{+}{-}18x} \\ \phantom{{2x^2 - x - 6}2x^3+}-10x^2 + 5x + 30 \\ \phantom{{2x^2 - x - 6}2x^3+}\underline{\underset{+}{-}10x^2 \underset{-}{+} 5x \underset{-}{+} 30} \\ \phantom{{2x^2 - x - 6}{2x^3+}{+5x^2222}}\times \end{array}$$

Hence, (6x3 - 13x2 - 13x + 30) ÷ (2x2 - x - 6) = 3x - 5

11(xiv)Exercise 11(B)

Divide:

4a2 + 12ab + 9b2 - 25c2 by 2a + 3b + 5c

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Dividing 4a2 + 12ab + 9b2 - 25c2 by 2a + 3b + 5c

$$\begin{array}{l} \phantom{2a + 3b + 5c)}{2a + 3b - 5c} \\ 2a + 3b + 5c\overline{\smash{\big)}4a^2 + 12ab + 9b^2 - 25c^2} \\ \phantom{2a + 3b + 5c}\underline{\underset{-}{}4a^2 \underset{-}{+}6ab \phantom{+ 9b^2 - 25c^2} \underset{-}{+}10ac} \\ \phantom{{2a + 3b + 5c}2x^3+}6ab - 10ac + 9b^2 - 25c^2 \\ \phantom{{2a + 3b + 5c}2x+}\underline{\underset{-}{}6ab \phantom{- 10ac} \underset{-}{+} 9b^2 \phantom{- 25c^2} \underset{-}{+} 15bc} \\ \phantom{{2a + 3b + 5c}{2x^3+}{+5x^2+}}-10ac - 25c^2 -15bc \\ \phantom{{2a + 3b + 5c}{2x^3+}{+5x^2+\enspace}}\underline{\underset{+}{-}10ac \underset{+}{-} 25c^2 \underset{+}{-} 15bc} \\ \phantom{{2a + 3b + 5c}{2x^3+}{+5x^2+\qquad}{-23x}}\times \end{array}$$

Hence, (4a2 + 12ab + 9b2 - 25c2) ÷ (2a + 3b + 5c) = 2a + 3b - 5c

11(xv)Exercise 11(B)

Divide:

16 + 8x + x6 - 8x3 - 2x4 + x2 by x + 4 - x3

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Dividing 16 + 8x + x6 - 8x3 - 2x4 + x2 by x + 4 - x3

⇒ Dividing x6 - 2x4 - 8x3 + x2 + 8x + 16 by -x3 + x + 4

$$\begin{array}{l} \phantom{-x^3 + x + 4)}{-x^3 + x + 4} \\ -x^3 + x + 4\overline{\smash{\big)}x^6 - 2x^4 - 8x^3 + x^2 + 8x + 16} \\ \phantom{-x^3 + x + 4}\underline{\underset{-}{}x^6 \underset{+}{-}\phantom{2}x^4 \underset{+}{-}4x^3} \\ \phantom{{-x^3 + x + 4}2x^3+}-x^4 - 4x^3 + x^2 + 8x + 16 \\ \phantom{{-x^3 + x + 4}2x+2}\underline{\underset{+}{-}x^4 \phantom{- 4x^3} \underset{-}{+} x^2 \underset{-}{+} 4x} \\ \phantom{{-x^3 + x + 4}{2x^3+}{+x+}}-4x^3 \phantom{+ x^2} + 4x + 16 \\ \phantom{{-x^3 + x + 4}{2x^3+}{+541)}}\underline{\underset{+}{-}4x^3 \phantom{+ x^2} \underset{+}{-} 4x \underset{-}{+} 16} \\ \phantom{{-x^3 + x + 4}{2x^3+}{+5x^2+\qquad}{-23x}}\times \end{array}$$

Hence, (16 + 8x + x6 - 8x3 - 2x4 + x2) ÷ (x + 4 - x3) = -x3 + x + 4

12(i)Exercise 11(B)

Find the quotient and the remainder (if any), when:

a3 - 5a2 + 8a + 15 is divided by a + 1.

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Dividing a3 - 5a2 + 8a + 15 by a + 1

$$\begin{array}{l} \phantom{a + 1)}{a^2 - 6a + 14} \\ a + 1\overline{\smash{\big)}a^3 - 5a^2 + 8a + 15} \\ \phantom{a + 1}\underline{\underset{-}{}a^3 \underset{-}{+}a^2} \\ \phantom{{a + 1}2x}-6a^2 +8a + 15 \\ \phantom{{a + 1}21x}\underline{\underset{+}{-}6a^2 \underset{+}{-} 6a} \\ \phantom{{a + 1}{2x^3+}{+5x^2+}}14a + 15 \\ \phantom{{a + 1}{2x^3+}{+5x^2}}\underline{\underset{+}{-}14a \underset{-}{+} 14} \\ \phantom{{a + 1}{a^3 - 5a^2 + 8a + 152}} 1 \end{array}$$

Quotient = a2 - 6a + 14

Remainder = 1

Verification:

Quotient x Divisor + Remainder

= (a2 - 6a + 14) $\times$ (a + 1) + 1

= a $\times$ (a2 - 6a + 14) + 1 $\times$ (a2 - 6a + 14) + 1

= a(1+2) - 6a(1+1) + 14a + a2 - 6a + 14 + 1

= a3 - 6a2 + 14a + a2 - 6a + 14 + 1

= a3 + (- 6a2 + a2) + (14a - 6a) + (14 + 1)

= a3 - 5a2 + 8a + 15

= Dividend

12(ii)Exercise 11(B)

Find the quotient and the remainder (if any), when:

3x4 + 6x3 - 6x2 + 2x - 7 is divided by x - 3.

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Dividing 3x4 + 6x3 - 6x2 + 2x - 7 by x - 3

$$\begin{array}{l} \phantom{x - 3)}{3x^3 + 15x^2 + 39x + 119} \\ x - 3\overline{\smash{\big)}3x^4 + 6x^3 - 6x^2 + 2x - 7} \\ \phantom{x - 3}\underline{\underset{-}{}3x^4 \underset{+}{-}9x^3} \\ \phantom{{x - 3)}{3x^4567}}15x^3 - 6x^2 + 2x - 7 \\ \phantom{{x - 3}{3x^456}}\underline{\underset{-}{+}15x^3 \underset{+}{-} 45x^2} \\ \phantom{{x - 3}{3x^456 + 15x^3 + }}39x^2 + 2x - 7 \\ \phantom{{x - 3}{3x^456 + 15x^3}}\underline{\underset{-}{+}39x^2 \underset{+}{-} 117x} \\ \phantom{{x - 3}{3x^456 + 15x^3 + 39x^2 +}}119x - 7 \\ \phantom{{x - 3}{3x^456 + 15x^3 + 39x^2}}\underline{\underset{-}{+}119x \underset{+}{-} 357} \\ \phantom{{x - 3}{3x^456 + 15x^3 + 39x^2 + 117x +}}350 \end{array}$$

Quotient = 3x3 + 15x2 + 39x + 119

Remainder = 350

Verification:

Quotient x Divisor + Remainder

= (3x3 + 15x2 + 39x + 119) $\times$ (x - 3) + 350

= x $\times$ (3x3 + 15x2 + 39x + 119) - 3 $\times$ (3x3 + 15x2 + 39x + 119) + 350

= 3x(3+1) + 15x(2+1) + 39x(1+1) + 119x - 9x3 - 45x2 - 117x - 357 + 350

= 3x4 + 15x3 + 39x2 + 119x - 9x3 - 45x2 - 117x - 357 + 350

= 3x4 + (15x3 - 9x3) + (39x2 - 45x2) + (119x - 117x) + (- 357 + 350)

= 3x4 + 6x3 - 6x2+ 2x - 7

= Dividend

12(iii)Exercise 11(B)

Find the quotient and the remainder (if any), when:

6x2 + x - 15 is divided by 3x + 5.

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(6x2 + x - 15) ÷ (3x + 5)

Dividing 6x2 + x - 15 by 3x + 5

$$\begin{array}{l} \phantom{3x + 5)}{2x - 3} \\ 3x + 5\overline{\smash{\big)}6x^2 + x - 15} \\ \phantom{3x + 5}\underline{\underset{-}{}6x^2 \underset{-}{+}10x} \\ \phantom{{3x + 5}6x^2 +}-9x - 15 \\ \phantom{{3x + 5}6x^2 +}\underline{\underset{+}{-}9x \underset{+}{-} 15} \\ \phantom{{3x + 5}6x^2 + 9x -} \times \end{array}$$

Quotient = 2x - 3

Remainder = 0

Verification:

Quotient x Divisor + Remainder

= (2x - 3) $\times$ (3x + 5) + 0

= 2x $\times$ (3x + 5) - 3 $\times$ (3x + 5)

= 6x(1+1) + 10x - 9x - 15

= 6x2 + (10x - 9x) - 15

= 6x2 + x - 15

= Dividend

13Exercise 11(B)

The area of a rectangle is x3 - 8x2 + 7 and one of its sides is x - 1. Find the length of the adjacent side.

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Area of the rectangle = x3 - 8x2 + 7

One side = (x - 1)

As we know the area of rectangle = One side x Other side

Other side = Area of rectangle ÷ One side

= (x3 - 8x2 + 7) ÷ (x - 1)

$$\begin{array}{l} \phantom{x - 1)}{x^2 - 7x - 7} \\ x - 1\overline{\smash{\big)}x^3 - 8x^2 + 7} \\ \phantom{x - 1}\underline{\underset{-}{}x^3 \underset{+}{-}x^2} \\ \phantom{{x - 1}12x}-7x^2 + 7 \\ \phantom{{x - 1}221x}\underline{\underset{+}{-}7x^2 \phantom{+ 7} \underset{-}{+} 7x} \\ \phantom{{x - 1}{2x^3+}{+5x}}-7x + 7 \\ \phantom{{x - 1}{2x^3+}{+5x^2}}\underline{\underset{+}{-}7x \underset{-}{+} 7} \\ \phantom{{x - 1}{2x^3+}{+5x^2}{-7x}} \times \end{array}$$

Hence, length of adjacent side is x2 - 7x - 7.

1(i)Exercise 11(C)

The value of $x - \overline{x - y}$ is:

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$x - \overline{x - y}$

= $x - x + y$

= $y$

Hence, option 3 is the correct option.

1(ii)Exercise 11(C)

(5x - 4y) - (5y - 4x) is equal to:

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(5x - 4y) - (5y - 4x)

= 5x - 4y - 5y + 4x

= (5x + 4x) + (-4x - 5y)

= 9x + (- 9y)

= 9x - 9y

= 9(x - y)

Hence, option 1 is the correct option.

1(iii)Exercise 11(C)

$x (y - x - \overline{x - y})$ is equal to:

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$x (y - x - \overline{x - y})$

= $x (y - x - x + y)$

= $x (2y - 2x)$

= $2x (y - x)$

Hence, option 2 is the correct option.

1(iv)Exercise 11(C)

$(2x - y) + \overline{2x - y}$ is equal to :

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$(2x - y) + \overline{2x - y}$

= $2x - y + 2x - y$

= $4x - 2y$

Hence, option 4 is the correct option.

1(v)Exercise 11(C)

x(y - z) + y(z - x) - z(y - x) is equal to:

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x(y - z) + y(z - x) - z(y - x)

= xy - xz + yz - xy - yz + xz

= (xy - xy) + (- xz + xz) + (yz - yz)

= 0 + 0 + 0

Hence, option 1 is the correct option.

2Exercise 11(C)

a2 - 2a + {5a2 - (3a - 4a2)}

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a2 - 2a + {5a2 - (3a - 4a2)}

= a2 - 2a + {5a2 - 3a + 4a2}

= a2 - 2a + {(5a2 + 4a2) - 3a}

= a2 - 2a + {9a2 - 3a}

= a2 - 2a + 9a2 - 3a

= (a2 + 9a2) + ( - 2a - 3a)

= 10a2 + (- 5a)

= 10a2 - 5a

Hence, a2 - 2a + {5a2 - (3a - 4a2)} = 10a2 - 5a

3Exercise 11(C)

$x - y - \lbrace x - y - (x + y) - \overline{x - y}\rbrace$

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$x - y - \lbrace x - y - (x + y) - \overline{x - y}\rbrace$

= $x - y - \lbrace x - y - (x + y) - x + y\rbrace$

= $x - y - \lbrace \cancel{x} - \cancel{y} - (x + y) - \cancel{x} + \cancel{y}\rbrace$

= $x - y - \lbrace -(x + y)\rbrace$

= $x - y - \lbrace - x - y\rbrace$

= $x - \cancel{y} + x + \cancel{y}$

= $2x$

Hence, $x - y - \lbrace x - y - (x + y) - \overline{x - y}\rbrace = 2x$

4Exercise 11(C)

-3(1 - x2) - 2{x2 - (3 - 2x2)}

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-3(1 - x2) - 2{x2 - (3 - 2x2)}

= -3(1 - x2) - 2{x2 - 3 + 2x2}

= -3(1 - x2) - 2{(x2 + 2x2) - 3}

= -3(1 - x2) - 2{3x2 - 3}

= -3 + 3x2 - 6x2 + 6

= (-3 + 6) + (3x2 - 6x2)

= 3 + (-3x2)

= 3 - 3x2

Hence, -3(1 - x2) - 2{x2 - (3 - 2x2)} = 3 - 3x2

5Exercise 11(C)

$2\lbrace m - 3(n + \overline{m - 2n})\rbrace$

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$2\lbrace m - 3(n + \overline{m - 2n})\rbrace$

= $2\lbrace m - 3(n + m - 2n)\rbrace$

= $2\lbrace m - 3((n - 2n) + m)\rbrace$

= $2\lbrace m - 3(-n + m)\rbrace$

= $2\lbrace m + 3n - 3m\rbrace$

= $2\lbrace (m - 3m) + 3n\rbrace$

= $2\lbrace -2m + 3n\rbrace$

= $-4m + 6n$

Hence, $2\lbrace m - 3(n + \overline{m - 2n})\rbrace = 6n - 4m$

6Exercise 11(C)

$3x - [3x - \lbrace 3x - (3x - \overline{3x - y})\rbrace]$

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$3x - [3x - \lbrace 3x - (3x - \overline{3x - y})\rbrace]$

= $3x - [3x - \lbrace 3x - (3x - 3x + y)\rbrace]$

= $3x - [3x - \lbrace 3x - (y)\rbrace]$

= $3x - [3x - \lbrace 3x - y\rbrace]$

= $3x - [3x - 3x + y]$

= $3x - [y]$

= $3x - y$

Hence, $3x - [3x - \lbrace 3x - (3x - \overline{3x - y})\rbrace] = 3x - y$

7Exercise 11(C)

$p^2x - 2\lbrace px - 3x(x^2 - \overline{3a - x^2})\rbrace$

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$p^2x - 2\lbrace px - 3x(x^2 - \overline{3a - x^2})\rbrace$

= $p^2x - 2\lbrace px - 3x(x^2 - 3a + x^2)\rbrace$

= $p^2x - 2\lbrace px - 3x((x^2 + x^2) - 3a)\rbrace$

= $p^2x - 2\lbrace px - 3x(2x^2 - 3a)\rbrace$

= $p^2x - 2\lbrace px - 6x^3 + 9ax\rbrace$

= $p^2x - 2px + 12x^3 - 18ax$

Hence, $p^2x - 2\lbrace px - 3x(x^2 - \overline{3a - x^2})\rbrace = p^2x - 2px + 12x^3 - 18ax$

8Exercise 11(C)

$2[6 + 4\lbrace m - 6(7 - \overline{n + p}) + q\rbrace]$

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$2[6 + 4\lbrace m - 6(7 - \overline{n + p}) + q\rbrace]$

= $2[6 + 4\lbrace m - 6(7 - n - p) + q\rbrace]$

= $2[6 + 4\lbrace m - 42 + 6n + 6p + q\rbrace]$

= $2[6 + 4m - 168 + 24n + 24p + 4q]$

= $2[(6 - 168) + 4m + 24n + 24p + 4q]$

= $2[-162 + 4m + 24n + 24p + 4q]$

= $-324 + 8m + 48n + 48p + 8q$

Hence, $2[6 + 4\lbrace m - 6(7 - \overline{n + p}) + q\rbrace] = 8m + 48n + 48p + 8q -324$

9Exercise 11(C)

$a - [a - \overline{b + a} - \lbrace a - (a - \overline{b - a})\rbrace]$

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$a - [a - \overline{b + a} - \lbrace a - (a - \overline{b - a})\rbrace]$

= $a - [a - \overline{b + a} - \lbrace a - (a - b + a)\rbrace]$

= $a - [a - \overline{b + a} - \lbrace a - (a + a - b)\rbrace]$

= $a - [a - \overline{b + a} - \lbrace a - (2a - b)\rbrace]$

= $a - [a - \overline{b + a} - \lbrace a - 2a + b\rbrace]$

= $a - [a - \overline{b + a} - \lbrace -a + b\rbrace]$

= $a - [a - \overline{b + a} + a - b]$

= $a - [a - b - a + a - b]$

= $a - [(a - a + a) + (- b - b)]$

= $a - [ a + (- 2b)]$

= $a - [ a - 2b]$

= $a - a + 2b$

= $2b$

Hence, $a - [a - \overline{b + a} - \lbrace a - (a - \overline{b - a})\rbrace] = 2b$

10Exercise 11(C)

$3x - [4x - \overline{3x - 5y} - 3\lbrace 2x - (3x - \overline{2x - 3y})\rbrace]$

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$3x - [4x - \overline{3x - 5y} - 3\lbrace 2x - (3x - \overline{2x - 3y})\rbrace]$

= $3x - [4x - \overline{3x - 5y} - 3\lbrace 2x - (3x - 2x + 3y)\rbrace]$

= $3x - [4x - \overline{3x - 5y} - 3\lbrace 2x - (x + 3y)\rbrace]$

= $3x - [4x - \overline{3x - 5y} - 3\lbrace 2x - x - 3y\rbrace]$

= $3x - [4x - \overline{3x - 5y} - 3\lbrace x - 3y\rbrace]$

= $3x - [4x - \overline{3x - 5y} - 3x + 9y]$

= $3x - [4x - 3x + 5y - 3x + 9y]$

= $3x - [(4x - 3x - 3x) + (5y + 9y)]$

= $3x - [-2x + 14y]$

= $3x + 2x - 14y$

= $5x - 14y$

Hence, $3x - [4x - \overline{3x - 5y} - 3\lbrace 2x - (3x - \overline{2x - 3y})\rbrace] = 5x - 14y$

11Exercise 11(C)

a5 ÷ a3 + 3a x 2a

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a5 ÷ a3 + 3a x 2a

= a(5-3) + 3a x 2a

= a2 + 3a x 2a

= a2 + 6a(1+1)

= a2 + 6a2

= 7a2

Hence, a5 ÷ a3 + 3a x 2a = 7a2

12Exercise 11(C)

x5 ÷ (x2 x y2) x y3

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$$\begin{aligned}x^5 ÷ (x^2 \times y^2) \times y^3\\[1em] = \frac{x^5}{x^2y^2} \times y^3\\[1em] = \frac{x^(5-2)}{y^2} \times y^3\\[1em] = \frac{x^3}{y^2} \times y^3\\[1em] = \frac{x^3y^3}{y^2}\\[1em] = x^3y^{3-2}\\[1em] = x^3y^1\\[1em]\end{aligned}$$

Hence, x5 ÷ (x2 $\times$ y2) $\times$ y3 = x3y

13Exercise 11(C)

(x5 ÷ x2) x y2 x y3

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(x5 ÷ x2) $\times$ y2 $\times$ y3

= x(5-2) $\times$ y2 $\times$ y3

= x3 $\times$ y2 $\times$ y3

= x3 $\times$ y(2+3)

= x3 $\times$ y5

Hence, (x5 ÷ x2) $\times$ y2 $\times$ y3 = x3y5

14Exercise 11(C)

(y3 - 5y2) ÷ y x (y - 1)

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(y3 - 5y2) ÷ y x (y - 1)

= (y3 ÷ y - 5y2 ÷ y) x (y - 1)

= (y(3-1) - 5y(2-1)) x (y - 1)

= (y2 - 5y1) x (y - 1)

= y2 x (y - 1) - 5y1 x (y - 1)

= y(2+1) - y2 - 5y(1+1) - 5y

= y3 - y2 - 5y2 - 5y

= y3 - 6y2 - 5y

Hence, (y3 - 5y2) ÷ y x (y - 1) = y3 - 6y2 - 5y

1(i)Test Yourself

(-18xy) - (-8xy) is equal to:

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(-18xy) - (-8xy)

= -18xy + 8xy

= - 10xy

Hence, option 2 is the correct option.

1(ii)Test Yourself

(9a + 7b - 6c) - (2a - 3b + 4c) is equal to:

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(9a + 7b - 6c) - (2a - 3b + 4c)

= 9a + 7b - 6c - 2a + 3b - 4c

= (9a - 2a) + (7b + 3b) + (- 6c - 4c)

= 7a + 10b + (-10c)

= 7a + 10b -10c

Hence, option 2 is the correct option.

1(iii)Test Yourself

-81a5b4c3 ÷ (-9a2b2c) is equal to:

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-81a5b4c3 ÷ (-9a2b2c)

= $\frac{-81}{-9}$ a(5-2)b(4-2)c(3-1)

= 9 a3b2c2

Hence, option 4 is the correct option.

1(iv)Test Yourself

$-(-pq - \overline{p^2 - pq})$ is equal to:

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$-(-pq - \overline{p^2 - pq})$

= $-(-pq - p^2 + pq)$

= $-((-pq + pq) - p^2)$

= $-(- p^2)$

= $p^2$

Hence, option 3 is the correct option.

1(v)Test Yourself

$x^3 - y^3 - x(y^2 + \overline{x^2 - z^2})$ is equal to:

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$x^3 - y^3 - x(y^2 + \overline{x^2 - z^2})$

= $x^3 - y^3 - x(y^2 + x^2 - z^2)$

= $x^3 - y^3 - xy^2 - x^3 + xz^2$

= $(x^3 - x^3) - y^3 - xy^2 + xz^2$

= $- y^3 - xy^2 + xz^2$

Hence, option 4 is the correct option.

1(vi)Test Yourself

Statement 1: The expression 2x4 - 3x2 + $\frac{7}{\text{x}}$, x ≠ 0 has no constant term.

Statement 2: In an algebraic expression in terms of one variable, the term(s) independent of the variable is called the constant.

Which of the following options is correct?

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Given :

2x4 - 3x2 + $\frac{7}{\text{x}}$

A constant term is a term that does not contain the variable in this case, x.

Thus, the expression contains no constant term.

So, statement 1 is true.

In an algebraic expression in terms of one variable, the term(s) independent of the variable is called the constant.

This is a standard definition in algebra: a constant term is the part of the expression that does not change with the variable i.e., it is independent of the variable.

So, statement 2 is true.

Hence, option 1 is the correct option.

1(vii)Test Yourself

Assertion (A) : 5x + y2 - x3, xy + yz + zx, x2 - x + 1 are all trinomials.

Reason (R) : An algebraic expression which contains three different terms is called a trinomials.

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An algebraic expression which contains three different terms is called a trinomial.

So, reason (R) is true.

Given, 5x + y2 - x3, xy + yz + zx, x2 - x + 1

All three expressions have three distinct terms.

So, assertion (A) is true and, reason (R) is the correct explanation of assertion (A).

Hence, option 1 is the correct option.

1(viii)Test Yourself

Assertion (A) : Refer the following algebraic expressions in terms of one variable : 3x + 9, 9 - $\frac{3}{\text{x}^2}$, 100.

Two of them are not polynomials in x.

Reason (R) : An algebraic expression is a polynomial if the degree of each term used in it is a whole number.

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An algebraic expression is a polynomial if the degree of each term used in it is a whole number.

So, reason (R) is true

A polynomial in one variable (say, x) must have:

  • Only non-negative integers (i.e., whole numbers) as exponents of x.

  • No negative or fractional powers.

So, reason (R) is true.

Given,

Algebraic expressions : 3x + 9, 9 - $\frac{3}{\text{x}^2}$, 100

3x + 9 and 100 (constant polynomial) both are polynomials, while 9 - $\frac{3}{\text{x}^2}$ is not as on taking the variable in numerator (9 - 3x-2) the power becomes negative.

So, assertion (A) is false.

Hence, option 4 is the correct option.

1(ix)Test Yourself

Assertion (A) : 2xyz + 3x2y is a cubic polynomial in three variables.

Reason (R) : An algebraic expression having two or more variables, the highest sum of the powers of all the variables in each term is taken as the degree of the polynomial, if this sum is a whole number.

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An algebraic expression having two or more variables, the highest sum of the powers of all the variables in each term taken as the degree of the polynomial if this sum is a whole number.

The maximum of these sums gives the degree. These powers must be whole numbers for it to be a valid polynomial.

So, reason (R) is true.

Given; 2xyz + 3x2y

Terms; 2xyz, 3x2y

For term 2xyz, degree = 1 + 1 + 1 = 3

For term 3x2y, degree = 2 + 1 = 3

The degree of a polynomial in multiple variables is the highest total degree among its terms.

Thus, the degree of this polynomial is 3.

Therefore, this is a cubic polynomial in three variables.

So, assertion (A) is true and, reason (R) is the correct explanation of assertion (A).

Hence, option 1 is the correct option.

1(x)Test Yourself

Assertion (A) : 2024x2yz is not a trinomial.

Reason (R) : For combining polynomials, the like terms of the given polynomials are combined together.

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A trinomial is an algebraic expression with exactly three terms.

Here, 2024x2yz is just a single term — a monomial.

Thus, the statement that it's not a trinomial is correct.

So, assertion (A) is true.

For combining polynomials, the like terms of the given polynomials are combined together.

Like terms are terms with the same variables raised to the same powers.

When combining polynomials, you add or subtract like terms.

So, reason (R) is true but, reason (R) does not explains assertion(A).

Hence, option 2 is the correct option.

2Test Yourself

In $\frac{5}{7}$ xy2z3, write the coefficient of:

(i) 5

(ii) $\frac{5}{7}$

(iii) 5x

(iv) xy2

(v) z3

(vi) xz3

(vii) 5xy2

(viii) $\frac{1}{7}$ yz

(ix) z

(x) yz2

(xi) 5xyz

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(i) Coefficient = $\frac{1}{7}$ xy2z3

(ii) Coefficient = xy2z3

(iii) Coefficient = $\frac{1}{7}$ y2z3

(iv) Coefficient = $\frac{5}{7}$ z3

(v) Coefficient = $\frac{5}{7}$ xy2

(vi) Coefficient = $\frac{5}{7}$ y2

(vii) Coefficient = $\frac{1}{7}$ z3

(viii) Coefficient = 5 xyz2

(ix) Coefficient = $\frac{5}{7}$ xy2z2

(x) Coefficient = $\frac{5}{7}$ xyz

(xi) Coefficient = $\frac{1}{7}$ yz2

3(i)Test Yourself

In each polynomial, given below, separate the like terms:

3xy, - 4yx2, 2xy2, 2.5x2y, - 8yx, - 3.2y2x and x2y

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Like terms are those terms which have the same variable raised to the same power.

Hence, 3xy,- 8yx ; 2y2x, - 3.2y2x ; -4x2y, 2.5x2y and x2y are like terms.

3(ii)Test Yourself

In each polynomial, given below, separate the like terms:

y2z3, xy2z3, - 5x2yz, - 4y2z3, - 8xz3y2, 3x2yz and 2z3y2

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Like terms are those terms which have the same variable raised to the same power.

Hence, y2z3, - 4y2z3 and 2z3y2; xy2z3, - 8xz3y2 ; - 5x2yz, 3x2yz are like terms.

4Test Yourself

The sides of a triangle are x2 - 3xy + 8, 4x2 + 5xy - 3 and 6 - 3x2 + 4xy. Find its perimeter.

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The sides of a triangle = (x2 - 3xy + 8), (4x2 + 5xy - 3) and (6 - 3x2 + 4xy)

Perimeter of triangle = sum of all its side.

(x2 - 3xy + 8) + (4x2 + 5xy - 3) + (6 - 3x2 + 4xy)

= x2 - 3xy + 8 + 4x2 + 5xy - 3 + 6 - 3x2 + 4xy

= (x2 + 4x2 - 3x2) + (- 3xy + 5xy + 4xy) + (- 3 + 6 + 8)

= 2x2 + 6xy + 11

Hence, perimeter of triangle = 2x2 + 6xy + 11

5Test Yourself

The perimeter of a triangle is 8y2 - 9y + 4 and its two sides are 3y2 - 5y and 4y2 + 12. Find its third side.

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The perimeter of a triangle = 8y2 - 9y + 4

Two sides are 3y2 - 5y and 4y2 + 12

Let the third side be S.

As we know that, perimeter of triangle = sum of all its side.

8y2 - 9y + 4 = (3y2 - 5y) + (4y2 + 12) + S

⇒ 8y2 - 9y + 4 = 3y2 - 5y + 4y2 + 12 + S

⇒ 8y2 - 9y + 4 = (3y2 + 4y2) - 5y + 12 + S

⇒ 8y2 - 9y + 4 = 7y2 - 5y + 12 + S

⇒ S = (8y2 - 9y + 4) - (7y2 - 5y + 12)

⇒ S = 8y2 - 9y + 4 - 7y2 + 5y - 12

⇒ S = (8y2 - 7y2) + (- 9y + 5y) + (4 - 12)

⇒ S = 1y2 - 4y - 8

Hence, the third side of triangle = (y2 - 4y - 8)

6Test Yourself

The two adjacent sides of a rectangle are 2x2 - 5xy + 3z2 and 4xy - x2 - z2. Find its perimeter.

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The two adjacent sides of a rectangle = (2x2 - 5xy + 3z2) and (4xy - x2 - z2)

As we know the perimeter of rectangle = 2 x (l + b)

= 2 $\times$ [(2x2 - 5xy + 3z2) + (4xy - x2 - z2)]

= 2 $\times$ [2x2 - 5xy + 3z2 + 4xy - x2 - z2]

= 2 $\times$ [(2x2 - x2) + (- 5xy + 4xy) + (3z2 - z2)]

= 2 $\times$ [x2 - 1xy + 2z2]

= 2 $\times$ x2 - 2 $\times$ 1xy + 2 $\times$ 2z2

= 2x2 - 2xy + 4z2

Hence, the perimeter of rectangle = 2x2 - 2xy + 4z2

7Test Yourself

What must be subtracted from 19x4 + 2x3 + 30x - 37 to get 8x4 + 22x3 - 7x - 60?

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Let A be the number that should be subtracted from 19x4 + 2x3 + 30x - 37 to get 8x4 + 22x3 - 7x - 60

(19x4 + 2x3 + 30x - 37) - A = (8x4 + 22x3 - 7x - 60)

⇒ (19x4 + 2x3 + 30x - 37) - (8x4 + 22x3 - 7x - 60) = A

⇒ A = 19x4 + 2x3 + 30x - 37 - 8x4 - 22x3 + 7x + 60

⇒ A = (19x4 - 8x4) + (2x3 - 22x3) + (30x + 7x) + (- 37 + 60)

⇒ A = 11x4 - 20x3 + 37x + 23

Hence, the number is 11x4 - 20x3 + 37x + 23.

8Test Yourself

How much smaller is 15x - 18y + 19z than 22x - 20y -13z +26?

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(22x - 20y -13z + 26) - (15x - 18y + 19z)

= 22x - 20y -13z + 26 - 15x + 18y - 19z

= (22x - 15x) + (- 20y + 18y) + (-13z - 19z) + 26

= 7x - 2y -32z + 26

Hence, (22x - 20y -13z +26) is less than (15x - 18y + 19z) by (7x - 2y -32z + 26)

9Test Yourself

How much bigger is 5x2y2 - 18xy2 - 10x2y than - 5x2 + 6x2y - 7xy?

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(5x2y2 - 18xy2 - 10x2y) - (- 5x2 + 6x2y - 7xy)

= 5x2y2 - 18xy2 - 10x2y + 5x2 - 6x2y + 7xy

= 5x2y2 - 18xy2 + (- 10x2y - 6x2y) + 5x2 + 7xy

= 5x2y2 - 18xy2 - 16x2y + 5x2 + 7xy

Hence, (5x2y2 - 18xy2 - 10x2y) is bigger than (- 5x2 + 6x2y - 7xy) by (5x2y2 - 18xy2 - 16x2y + 5x2 + 7xy)

10Test Yourself

If x = 2 and y = 1 ; find the value of (-4x2y3) x (-5x2y5).

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(-4x2y3) $\times$ (-5x2y5)

= (-4) $\times$ (-5)x(2+2)y(3+5)

= 20 x4y8

When x = 2 and y = 1,

= 20 x 24 x 18

= 20 x 16 x 1

= 320

Hence, if x = 2 and y = 1 ; the value of (-4x2y3) x (-5x2y5) = 320.

11(i)Test Yourself

Evaluate:

(3x - 2) (x + 5) for x = 2.

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(3x - 2) (x + 5)

= 3x (x + 5) - 2 (x + 5)

= 3x(1+1) + 15x - 2x - 10

= 3x2 + (15x - 2x) - 10

= 3x2 + 13x - 10

For x = 2

3 x 22 + 13 x 2 - 10

= 3 x 4 + 26 - 10

= 12 + 26 - 10

= 38 - 10

= 28

Hence, for x = 2, the value of (3x - 2) (x + 5) is 28.

11(ii)Test Yourself

Evaluate:

(2x - 5y) (2x + 3y) for x = 2 and y = 3.

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(2x - 5y) (2x + 3y)

= 2x (2x + 3y) - 5y (2x + 3y)

= 4x(1+1) + 6xy - 10xy - 15y(1+1)

= 4x2 + (6xy - 10xy) - 15y2

= 4x2 - 4xy - 15y2

For x = 2, y = 3

4 x 22 - 4 x 2 x 3 - 15 x 32

= 4 x 4 - 4 x 2 x 3 - 15 x 9

= 16 - 24 - 135

= - 143

Hence, for x = 2, y = 3, the value (2x - 5y) (2x + 3y) = - 143.

11(iii)Test Yourself

Evaluate:

xz (x2 + y2) for x = 2, y = 1 and z = 1.

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xz (x2 + y2)

= x(2+1)z + xzy2

= x3z + xzy2

For x = 2, y = 1 and z = 1

23 x 1 + 2 x 1 x 12

= 8 x 1 + 2 x 1 x 1

= 8 + 2

= 10

Hence, for x = 2, y = 1 and z = 1, the value of xz (x2 + y2) is 10.

12(i)Test Yourself

Evaluate:

x(x - 5) + 2 for x = 1.

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x(x - 5) + 2

= x2 - 5x + 2

For x = 1

= 12 - 5 x 1 + 2

= 1 - 5 + 2

= - 2

Hence, for x = 1, the value of x(x - 5) + 2 is - 2.

12(ii)Test Yourself

Evaluate:

xy2(x - 5y) + 1 for x = 2 and y = 1.

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xy2(x - 5y) + 1

= x(1+1)y2 - 5xy(2+1) + 1

= x2y2 - 5xy3 + 1

For x = 2 and y = 1,

22 x 12 - 5 x 2 x 13 + 1

= 4 x 1 - 5 x 2 x 1 + 1

= 4 - 10 + 1

= - 5

Hence, for x = 2 and y = 1, the value of [xy2(x - 5y) + 1] is - 5.

12(iii)Test Yourself

Evaluate:

2x(3x - 5) - 5(x - 2) - 18 for x = 2.

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2x(3x - 5) - 5(x - 2) - 18

= 6x(1+1) - 10x - 5x + 10 - 18

= 6x2 + (- 10x - 5x) + (10 - 18)

= 6x2 - 15x - 8

For x = 2,

= 6 x 22 - 15 x 2 - 8

= 6 x 4 - 15 x 2 - 8

= 24 - 30 - 8

= - 14

Hence, for x = 2, the value of [2x(3x - 5) - 5(x - 2) - 18] is - 14.

13Test Yourself

Multiply and then verify:

-3x2y2 and (x - 2y) for x = 1 and y = 2.

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(-3x2y2) $\times$ (x - 2y)

= (-3x2y2) $\times$ x - (-3x2y2) $\times$ 2y

= (-3x(2+1)y2) - (-6x2y(2+1))

= -3x3y2 + 6x2y3

For x = 1 and y = 2

(-3x2y2) $\times$ (x - 2y) = -3x3y2 + 6x2y3

Taking LHS:

(-3x2y2) $\times$ (x - 2y)

= (-3 x 12 x 22) x (1 - 2 x 2)

= (-3 x 1 x 4) x (1 - 4)

= (-12) x (- 3)

= 36

Now, taking RHS:

-3x3y2 + 6x2y3

= -3 x 13 x 22 + 6 x 12 x 23

= -3 x 1 x 4 + 6 x 1 x 8

= -12 + 48

= 36

Hence, LHS = RHS.

14(i)Test Yourself

Multiply:

2x2 - 4x + 5 by x2 + 3x - 7

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(2x2 - 4x + 5) $\times$ (x2 + 3x - 7)

= 2x2 $\times$ (x2 + 3x - 7) - 4x $\times$ (x2 + 3x - 7) + 5 $\times$ (x2 + 3x - 7)

= 2x(2+2) + 6x(2+1) - 14x2 - 4x(1+2) - 12x(1+1) + 28x + 5x2 + 15x - 35

= 2x4 + 6x3 - 14x2 - 4x3 - 12x2 + 28x + 5x2 + 15x - 35

= 2x4 + (6x3 - 4x3) + (- 14x2 - 12x2 + 5x2) + (28x + 15x) - 35

= 2x4 + 2x3 - 21x2 + 43x - 35

Hence, (2x2 - 4x + 5) $\times$ (x2 + 3x - 7) = 2x4 + 2x3 - 21x2 + 43x - 35

14(ii)Test Yourself

Multiply:

(ab - 1) (3 - 2ab)

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(ab - 1) (3 - 2ab)

= ab (3 - 2ab) - 1 (3 - 2ab)

= 3ab - 2a(1+1)b(1+1) - 3 + 2ab

= 3ab - 2a2b2 - 3 + 2ab

= (3ab + 2ab) - 2a2b2 - 3

= 5ab - 2a2b2 - 3

Hence, (ab - 1) (3 - 2ab) = 5ab - 2a2b2 - 3

15Test Yourself

Simplify:

(5 - x) (6 - 5x) (2 - x).

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(5 - x) (6 - 5x) (2 - x)

= [5 (6 - 5x) - x (6 - 5x)](2 - x)

= [30 - 25x - 6x + 5x(1+1)](2 - x)

= [30 + (- 25x - 6x) + 5x2](2 - x)

= [30 - 31x + 5x2](2 - x)

= 2 (30 - 31x + 5x2) - x (30 - 31x + 5x2)

= 60 - 62x + 10x2 - 30x + 31x(1+1) - 5x(2+1)

= 60 - 62x + 10x2 - 30x + 31x2 - 5x3

= 60 + (- 62x - 30x) + (10x2 + 31x2) - 5x3

= 60 - 92x + 41x2 - 5x3

Hence, (5 - x) (6 - 5x) (2 - x) = 60 - 92x + 41x2 - 5x3

16Test Yourself

The product of two numbers is 16x4 -1. If one number is 2x - 1, find the other.

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The product = (16x4 -1)

One number = (2x - 1)

Let the other number be A.

(2x - 1) $\times$ A = (16x4 -1)

⇒ A = $\frac{(16x^4 - 1)}{(2x - 1)}$

⇒ A = $\frac{(4x^2 - 1)(4x^2 + 1)}{(2x - 1)}$

⇒ A = $\frac{(2x - 1)(2x + 1)(4x^2 + 1)}{(2 - 1)}$

⇒ A = $\frac{\cancel{(2x - 1)}(2x + 1)(4x^2 + 1)}{\cancel{(2x - 1)}}$

⇒ A = (2x + 1)(4x2 + 1)

⇒ A = 2x(4x2 + 1) + 1(4x2 + 1)

⇒ A = 8x(2+1) + 2x + 4x2 + 1

⇒ A = 8x3 + 4x2 + 2x + 1

Hence, the other number is 8x3 + 4x2 + 2x + 1.

17Test Yourself

Divide x6 - y6 by the product of x2 + xy + y2 and x - y.

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The product of (x2 + xy + y2) and (x - y)

= (x2 + xy + y2) $\times$ (x - y)

= x $\times$ (x2 + xy + y2) - y $\times$ (x2 + xy + y2)

= x(1+2) + x(1+1)y + xy2 - x2y - xy(1+1) - y(1+2)

= x3 + x2y + xy2 - x2y - xy2 - y3

= x3 + (x2y - x2y) + (xy2 - xy2) - y3

= x3 - y3

Now, (x6 - y6) ÷ ( x3 - y3)

$$\begin{array}{l} \phantom{x^3 - y^3)}{x^3 + y^3} \\ x^3 - y^3\overline{\smash{\big)}x^6 - y^6 \phantom{+ x^3y^3}} \\ \phantom{x^3 - y^3}\underline{\underset{-}{}x^6 \phantom{- y^6} \underset{+}{-}x^3y^3} \\ \phantom{{x^3 - y^3}6x^2 +}x^3y^3 - y^6 \\ \phantom{{x^3 - y^3}6x^21}\underline{\underset{-}{+}x^3y^3 \underset{+}{-} y^6} \\ \phantom{{x^3 - y^3}6x^2 + 9x -} \times \end{array}$$

Hence, the answer is (x3 + y3)

18Test Yourself

$3a \times [8b ÷ 4 - 6\lbrace a - (5a - \overline{3b - 2a})\rbrace]$

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$3a \times [8b ÷ 4 - 6\lbrace a - (5a - \overline{3b - 2a})\rbrace]$

= $3a \times [8b ÷ 4 - 6\lbrace a - (5a - 3b + 2a)\rbrace]$

= $3a \times [8b ÷ 4 - 6\lbrace a - (5a + 2a - 3b )\rbrace]$

= $3a \times [8b ÷ 4 - 6\lbrace a - (7a - 3b )\rbrace]$

= $3a \times [8b ÷ 4 - 6\lbrace a - 7a + 3b \rbrace]$

= $3a \times [8b ÷ 4 - 6\lbrace -6a + 3b \rbrace]$

= $3a \times [8b ÷ 4 + 36a - 18b ]$

= $3a \times [2b + 36a - 18b]$

= $3a \times [2b - 18b + 36a]$

= $3a \times [-16b + 36a]$

= $-48ab + 108a^2$

Hence, $3a \times [8b ÷ 4 - 6\lbrace a - (5a - \overline{3b - 2a})\rbrace] = 108a^2 - 48ab$

19Test Yourself

7x + 4{x2 ÷ (5x ÷ 10)} - 3{2 - x3 ÷ (3x2 ÷ x)}

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7x + 4{x2 ÷ (5x ÷ 10)} - 3{2 - x3 ÷ (3x2 ÷ x)}

= 7x + 4{x2 ÷ (5x ÷ 10)} - 3{2 - x3 ÷ 3x}

= 7x + 4{x2 ÷ (5x ÷ 10)} - 3{2 - $\frac{\text{x}^2}{3}$}

= 7x + 4{x2 ÷ (5x ÷ 10)} - 6 + $\frac{3\text{x}^2}{3}$

= 7x + 4{x2 ÷ $\frac{5\text{x}}{10}$} - 6 + x2

= 7x + 4{x2 ÷ $\frac{\text{x}}{2}$} - 6 + x2

= 7x + 4{$\frac{2\text{x}^2}{\text{x}}$} - 6 + x2

= 7x + 4 x 2x - 6 + x2

= 7x + 8x - 6 + x2

= x2 + 15x - 6

Hence, the answer is x2 + 15x - 6

Press ↓ to reveal a solution and move to the next question. Back to Selina Solutions Concise Mathematics Class 8 ICSE.