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