Geometrical Constructions

ICSE Class 6 Mathematics · Solutions for Class 6 RS Aggarwal ICSE Foundation Mathematics · 25 solved questions

Exercise
1(i)Exercise 22

Construct the angle 36° using protractor.

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Steps of construction :

  1. Draw a ray OA.

  2. Keep the protractor with its central point at O and the horizontal edge along OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. On this scale, mark a point B against 36° mark and remove the protractor.

  5. Join O and B.

Construct the angle 36° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 36°.

1(ii)Exercise 22

Construct the angle 58° using protractor.

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Steps of construction :

  1. Draw a ray OA.

  2. Keep the protractor with its central point at O and the horizontal edge along OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. On this scale, mark a point B against 58° mark and remove the protractor.

  5. Join O and B.

Construct the angle 58° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 58°.

1(iii)Exercise 22

Construct the angle 90° using protractor.

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Steps of construction :

  1. Draw a ray OA.

  2. Keep the protractor with its central point at O and the horizontal edge along OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. On this scale, mark a point B against 90° mark and remove the protractor.

  5. Join O and B.

Construct the angle 90° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 90°.

1(iv)Exercise 22

Construct the angle 105° using protractor.

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Steps of construction :

  1. Draw a ray OA and extend it on the left of O to a point A′.

  2. Keep the protractor with its central point at O and the horizontal edge along A′OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. Move from right to left, starting with 0°, and mark a point B against 105° mark. Remove the protractor.

  5. Join O and B.

Construct the angle 105° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 105°.

1(v)Exercise 22

Construct the angle 45° using protractor.

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Steps of construction :

  1. Draw a ray OA.

  2. Keep the protractor with its central point at O and the horizontal edge along OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. On this scale, mark a point B against 45° mark and remove the protractor.

  5. Join O and B.

Construct the angle 45° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 45°.

1(vi)Exercise 22

Construct the angle 125° using protractor.

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Steps of construction :

  1. Draw a ray OA and extend it on the left of O to a point A′.

  2. Keep the protractor with its central point at O and the horizontal edge along A′OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. Move from right to left, starting with 0°, and mark a point B against 125° mark. Remove the protractor.

  5. Join O and B.

Construct the angle 125° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 125°.

1(vii)Exercise 22

Construct the angle 20° using protractor.

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Steps of construction :

  1. Draw a ray OA.

  2. Keep the protractor with its central point at O and the horizontal edge along OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. On this scale, mark a point B against 20° mark and remove the protractor.

  5. Join O and B.

Construct the angle 20° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 20°.

1(viii)Exercise 22

Construct the angle 140° using protractor.

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Steps of construction :

  1. Draw a ray OA and extend it on the left of O to a point A′.

  2. Keep the protractor with its central point at O and the horizontal edge along A′OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. Move from right to left, starting with 0°, and mark a point B against 140° mark. Remove the protractor.

  5. Join O and B.

Construct the angle 140° using protractor. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of 140°.

2Exercise 22

Draw ∠AOB = 65° using a protractor. Now, using ruler and compasses, construct ∠XOY = ∠AOB.

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Steps of construction :

  1. Draw a ray OA.

  2. Keep the protractor with its central point at O and the horizontal edge along OA.

  3. Look at the scale with 0° mark of the protractor lying on OA.

  4. On this scale, mark a point B against 65° mark and remove the protractor.

  5. Join O and B. Then, ∠AOB = 65°.

  6. With O as centre and any radius, draw an arc, cutting OA and OB at P and Q respectively.

  7. Draw any ray OX.

  8. With O as centre and radius equal to OP, draw an arc LM, cutting OX at M.

  9. With M as centre and radius equal to PQ, draw an arc, cutting LM at N.

  10. Join O and N and produce it to make the ray OY.

Draw ∠AOB = 65° using a protractor. Now, using ruler and compasses, construct ∠XOY = ∠AOB. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

∠XOY = ∠AOB = 65°

Hence, ∠XOY is the required angle equal to ∠AOB.

3Exercise 22

Draw ∠XOY = 53° using a protractor. Bisect ∠XOY using ruler and compasses.

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Steps of construction :

  1. Draw a ray OX.

  2. Keep the protractor with its central point at O and the horizontal edge along OX.

  3. Look at the scale with 0° mark of the protractor lying on OX.

  4. On this scale, mark a point Y against 53° mark and remove the protractor.

  5. Join O and Y. Then, ∠XOY = 53°.

  6. With O as centre and any convenient radius, draw an arc, cutting OX and OY at P and Q respectively.

  7. With P as centre and radius slightly more than $\frac{1}{2}$ PQ, draw an arc in the interior of ∠XOY.

  8. With Q as centre and the same radius (as in step 7), draw another arc, cutting the previous arc at Z.

  9. Draw OZ.

Draw ∠XOY = 53° using a protractor. Bisect ∠XOY using ruler and compasses. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

∠XOZ = ∠YOZ = $\frac{1}{2}$ ∠XOY = $\frac{1}{2}$ × 53° = 26.5°

Hence, OZ is the required bisector of ∠XOY.

4Exercise 22

Draw ∠POQ = 110° using a protractor. Bisect ∠POQ using ruler and compasses.

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Steps of construction :

  1. Draw a ray OP and extend it on the left of O to a point P′.

  2. Keep the protractor with its central point at O and the horizontal edge along P′OP.

  3. Look at the scale with 0° mark of the protractor lying on OP.

  4. Move from right to left, starting with 0°, and mark a point Q against 110° mark. Remove the protractor.

  5. Join O and Q. Then, ∠POQ = 110°.

  6. With O as centre and any convenient radius, draw an arc, cutting OP and OQ at M and N respectively.

  7. With M as centre and radius slightly more than $\frac{1}{2}$ MN, draw an arc in the interior of ∠POQ.

  8. With N as centre and the same radius (as in step 7), draw an arc cutting the previous arc at R.

  9. Draw OR.

Draw ∠POQ = 110° using a protractor. Bisect ∠POQ using ruler and compasses. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

∠POR = ∠QOR = $\frac{1}{2}$ ∠POQ = $\frac{1}{2}$ × 110° = 55°

Hence, OR is the required bisector of ∠POQ.

5Exercise 22

Draw a line segment AB = 5.3 cm. Using ruler and compasses, draw the perpendicular bisector of AB.

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Steps of construction :

  1. Draw a line segment AB = 5.3 cm.

  2. With A as centre and radius more than $\frac{1}{2}$ AB, draw one arc above AB and one arc below AB.

  3. With B as centre and the same radius as in step 2, draw other arcs, cutting the previous arcs at M and N.

  4. Join M and N, cutting AB at P.

Draw a line segment AB = 5.3 cm. Using ruler and compasses, draw the perpendicular bisector of AB. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Here, AP = PB = $\frac{1}{2}$ AB = 2.65 cm and ∠MPB = 90°.

Hence, MPN is the required perpendicular bisector of the given line segment AB.

6Exercise 22

Draw a line segment AB = 4.8 cm. Take a point P outside AB. From P, draw PQ ⊥ AB, using ruler and compasses.

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Steps of construction :

  1. Draw a line segment AB = 4.8 cm.

  2. Take a point P outside AB.

  3. With P as centre and any convenient radius, draw an arc, cutting AB at M and N.

  4. With M as centre and radius more than $\frac{1}{2}$ MN, draw an arc, below the line AB.

  5. With N as centre and the same radius (as in step 4), draw another arc, cutting the first arc at Q.

  6. Join P and Q, meeting AB at X.

Draw a line segment AB = 4.8 cm. Take a point P outside AB. From P, draw PQ ⊥ AB, using ruler and compasses. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, PQ is the required perpendicular from P to AB.

7Exercise 22

Draw a line segment AB = 5.2 cm. Take a point C on AB such that AC = 3 cm. From C, draw CD ⊥ AB using ruler and compasses.

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Given, AB = 5.2 cm and AC = 3 cm.

Steps of construction :

  1. Draw a line segment AB = 5.2 cm.

  2. From AB, cut off AC = 3 cm.

  3. With C as centre and a convenient radius, draw a semi-circle, cutting AB at M and N.

  4. With M as centre and radius more than $\frac{1}{2}$ MN, draw an arc.

  5. With N as centre and the same radius (as in step 4), draw another arc, cutting the previous arc at D.

  6. Join D and C.

Draw a line segment AB = 5.2 cm. Take a point C on AB such that AC = 3 cm. From C, draw CD ⊥ AB using ruler and compasses. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Here, ∠DCA = ∠DCB = 90°.

Hence, CD is the required perpendicular to AB at the point C.

8(i)Exercise 22

Using ruler and compasses, construct an angle of 60°.

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Steps of construction :

  1. Draw any ray OA.

  2. With O as centre and any convenient radius, draw an arc MN, cutting OA at M.

  3. With M as centre and the same radius (as in step 2), draw an arc, cutting the arc MN at P.

  4. Join O and P and produce it to B.

Using ruler and compasses, construct an angle of 60°. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the required angle of measure 60°.

8(ii)Exercise 22

Using ruler and compasses, construct an angle of 120°.

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Steps of construction :

  1. Draw any ray OA.

  2. With O as centre and any convenient radius, draw an arc MN (nearly a semi-circle), cutting OA at M.

  3. With M as centre and the same radius (as in step 2), draw an arc, cutting arc MN at P.

  4. With P as centre and the same radius (as in step 2), draw an arc, cutting arc MN at Q.

  5. Join O and Q and produce it to D.

Using ruler and compasses, construct an angle of 120°. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOD is the required angle whose measure is 120°.

8(iii)Exercise 22

Using ruler and compasses, construct an angle of 30°.

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As, 30° = $\frac{1}{2}$ × 60°

Steps of construction :

  1. Draw any ray OA.

  2. With O as centre and any convenient radius, draw an arc MN, cutting OA at M.

  3. With M as centre and the same radius (as in step 2), draw an arc, cutting arc MN at P.

  4. Join O and P and produce it to B. Then, ∠AOB = 60°.

  5. With M as centre and radius slightly more than $\frac{1}{2}$ MP, draw an arc in the interior of ∠AOB.

  6. With P as centre and the same radius (as in step 5), draw another arc, cutting the previous arc at C.

  7. Draw ray OC.

Using ruler and compasses, construct an angle of 30°. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

∠AOC = $\frac{1}{2}$ ∠AOB = $\frac{1}{2}$ × 60° = 30°

Hence, ∠AOC is the required angle whose measure is 30°.

8(iv)Exercise 22

Using ruler and compasses, construct an angle of 90°.

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Steps of construction :

  1. Draw any ray OA.

  2. With O as centre and any convenient radius, draw an arc MN (nearly a semi-circle), cutting OA at M.

  3. With M as centre and the same radius (as in step 2), draw an arc, cutting arc MN at P.

  4. With P as centre and the same radius (as in step 2), draw an arc, cutting arc MN at Q.

  5. With P as centre and radius slightly more than $\frac{1}{2}$ PQ, draw an arc above arc MN.

  6. With Q as centre and the same radius (as in step 5), draw another arc, cutting the previous arc at B.

  7. Draw ray OB.

Using ruler and compasses, construct an angle of 90°. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, ∠AOB is the desired angle whose measure is 90°.

8(v)Exercise 22

Using ruler and compasses, construct an angle of 45°.

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As, 45° = $\frac{1}{2}$ × 90°

Steps of construction :

  1. Draw any ray OA.

  2. With O as centre and any convenient radius, draw an arc MN (nearly a semi-circle), cutting OA at M.

  3. With M as centre and the same radius (as in step 2), draw an arc, cutting arc MN at P.

  4. With P as centre and the same radius (as in step 2), draw an arc, cutting arc MN at Q.

  5. With P as centre and radius slightly more than $\frac{1}{2}$ PQ, draw an arc above arc MN.

  6. With Q as centre and the same radius (as in step 5), draw another arc, cutting the previous arc at B.

  7. Draw ray OB. Then, ∠AOB = 90°.

  8. Let OB cut the arc MN at R.

  9. With M and R as centres and radius more than $\frac{1}{2}$ MR, draw two arcs which cut each other at C.

  10. Draw ray OC. Then, OC is the bisector of ∠AOB.

Using ruler and compasses, construct an angle of 45°. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

∠AOC = $\frac{1}{2}$ ∠AOB = $\frac{1}{2}$ × 90° = 45°

Hence, ∠AOC is the desired angle of measure 45°.

9Exercise 22

Draw a line segment AB = 4.6 cm. Construct ∠BAC = 30° and ∠ABC = 60°. Measure ∠ACB.

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Given, AB = 4.6 cm, ∠BAC = 30° and ∠ABC = 60°.

Steps of construction :

  1. Draw a line segment AB = 4.6 cm.

  2. With A as centre and any convenient radius, draw an arc, cutting AB at M.

  3. With M as centre and the same radius (as in step 2), draw an arc, cutting the previous arc at P. Then, ray AP makes an angle of 60° with AB.

  4. With M as centre and radius slightly more than $\frac{1}{2}$ MP, draw an arc in the interior of the angle.

  5. With P as centre and the same radius (as in step 4), draw another arc, cutting the previous arc at R.

  6. Draw ray AR. Then, ∠BAR = $\frac{1}{2}$ × 60° = 30°.

  7. With B as centre and any convenient radius, draw an arc, cutting BA at N.

  8. With N as centre and the same radius (as in step 7), draw an arc, cutting the previous arc at S.

  9. Join B and S and produce it to meet AR at C. Then, ∠ABC = 60°.

Draw a line segment AB = 4.6 cm. Construct ∠BAC = 30° and ∠ABC = 60°. Measure ∠ACB. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

On measuring, we get :

∠ACB = 90°

Hence, ABC is the required triangle with ∠BAC = 30° and ∠ABC = 60°.

10Exercise 22

Draw a circle of radius 5 cm using compasses.

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Steps of construction :

  1. Fix a sharp pencil in the pencil-holding arm of the compasses in such a way that the metal tip of the compasses and the sharp end of the pencil are in the same level.

  2. Put the metal tip of the compasses at 0 cm mark of the scale and open the other arm in such a way that the pencil end touches the 5 cm mark on the scale. Now, remove the open compasses from the scale.

  3. Mark a point O on the plane of the paper.

  4. Rest the metal tip of the compasses at O and hold the head of the compasses firmly such that the pencil end touches the paper.

  5. Move the pencil around so that it traces a circle.

Draw a circle of radius 5 cm using compasses. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, the circle so obtained is the required circle with centre O and radius 5 cm.

11Exercise 22

Take a point O on a paper. Draw a circle with centre O and radius 4.3 cm.

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Steps of construction :

  1. Fix a sharp pencil in the pencil-holding arm of the compasses in such a way that the metal tip of the compasses and the sharp end of the pencil are in the same level.

  2. Put the metal tip of the compasses at 0 cm mark of the scale and open the other arm in such a way that the pencil end touches the 4.3 cm mark on the scale. Now, remove the open compasses from the scale.

  3. Mark a point O on the plane of the paper.

  4. Rest the metal tip of the compasses at O and hold the head of the compasses firmly such that the pencil end touches the paper.

  5. Move the pencil around so that it traces a circle.

Take a point O on a paper. Draw a circle with centre O and radius 4.3 cm. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, the circle so obtained is the required circle with centre O and radius 4.3 cm.

12Exercise 22

Mark any two points P and Q on a paper. Using compasses, draw a circle with centre P and passing through Q.

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Steps of construction :

  1. Mark any two points P and Q on the paper.

  2. Put the metal tip of the compasses at P and open the other arm in such a way that the pencil end touches the point Q. Then, the radius taken is PQ.

  3. Rest the metal tip of the compasses at P and hold the head of the compasses firmly such that the pencil end touches the paper at Q.

  4. Move the pencil around so that it traces a circle.

Mark any two points P and Q on a paper. Using compasses, draw a circle with centre P and passing through Q. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Since the radius of the circle is PQ, the point Q lies on the circle.

Hence, the circle so obtained is the required circle with centre P and passing through Q.

13Exercise 22

Mark any three points O, P, Q. Draw a circle with centre O and which contains P in its interior and Q in its exterior.

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Steps of construction :

  1. Mark any three points O, P and Q on the paper such that OP < OQ.

  2. Measure OP and OQ.

  3. Open the compasses to a radius r which is greater than OP and smaller than OQ, i.e., OP < r < OQ.

  4. Rest the metal tip of the compasses at O and hold the head of the compasses firmly such that the pencil end touches the paper.

  5. Move the pencil around so that it traces a circle.

Mark any three points O, P, Q. Draw a circle with centre O and which contains P in its interior and Q in its exterior. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Since OP < r, the point P lies in the interior of the circle.

Since OQ > r, the point Q lies in the exterior of the circle.

Hence, the circle so obtained is the required circle with centre O, containing P in its interior and Q in its exterior.

14Exercise 22

Draw a line segment AB of length 6 cm. Draw a circle with AB as diameter. In this circle draw a chord of length 4 cm. Shade the minor segment of the circle.

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Steps of construction :

  1. Draw a line segment AB = 6 cm.

  2. With A as centre and radius more than $\frac{1}{2}$ AB, draw one arc above AB and one arc below AB.

  3. With B as centre and the same radius as in step 2, draw other arcs, cutting the previous arcs at M and N.

  4. Join M and N, cutting AB at C. Then, C is the mid-point of AB and CA = CB = 3 cm.

  5. With C as centre and radius CA, draw a circle. This circle has AB as its diameter.

  6. Take a point P on the circle.

  7. With P as centre and radius 4 cm, draw an arc to cut the circle at Q.

  8. Join P and Q. Then, PQ is a chord of length 4 cm.

  9. Shade the smaller region bounded by the chord PQ and the minor arc PQ.

Draw a line segment AB of length 6 cm. Draw a circle with AB as diameter. In this circle draw a chord of length 4 cm. Shade the minor segment of the circle. Geometrical Constructions, R.S. Aggarwal Mathematics Solutions ICSE Class 6.

Hence, PQ is the required chord of length 4 cm and the shaded region is the minor segment of the circle.

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