Question
If $A=\left[\begin{array}{ll}1 & 4 \\ 2 & 3\end{array}\right]$ and $B=\left[\begin{array}{ll}1 & 2 \\ 3 & 1\end{array}\right]$ Compute $3 A+4 B$
✓
Answer
$\begin{aligned} & A=\left[\begin{array}{ll}1 & 4 \\ 2 & 3\end{array}\right] \\ & B=\left[\begin{array}{ll}1 & 2 \\ 3 & 1\end{array}\right] \\ & 3 A+4 B=3\left[\begin{array}{ll}1 & 4 \\ 2 & 3\end{array}\right]+4\left[\begin{array}{ll}1 & 2 \\ 3 & 1\end{array}\right] \\ & =\left[\begin{array}{cc}3 & 12 \\ 6 & 9\end{array}\right]+\left[\begin{array}{cc}4 & 8 \\ 12 & 4\end{array}\right] \\ & =\left[\begin{array}{cc}3+4 & 12+8 \\ 6+12 & 9+4\end{array}\right] \\ & =\left[\begin{array}{cc}7 & 20 \\ 18 & 13\end{array}\right] .\end{aligned}$
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