1(ix)
If matrix A = $$\begin{bmatrix} -1 & 2 \end{bmatrix}$$ and matrix B = $$\begin{bmatrix} 3 \\ 4 \end{bmatrix}$$, then matrix AB is equal to:
$$1. \begin{bmatrix} -3 \end{bmatrix}$$
$$2. \begin{bmatrix} 8 \end{bmatrix}$$
$$3. \begin{bmatrix} 5 \end{bmatrix}$$
$$4. \begin{bmatrix} -1 & 2 \\ 3 & 4 \end{bmatrix}$$
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Calculating,
$$\Rightarrow AB = \begin{bmatrix} -1 & 2 \\ \end{bmatrix}\begin{bmatrix} 3 \\ 4 \end{bmatrix} \\[1em] = \begin{bmatrix} -1 \times 3 + 2 \times 4 \\ \end{bmatrix} \\[1em] = \begin{bmatrix} -3 + 8 \\ \end{bmatrix} \\[1em] = \begin{bmatrix} 5 \end{bmatrix}.$$
Hence, option 3 is the correct option.