Question

Evaluate UV if possible.

Answer 1

Answer: B

Explanation:

Multiply U and V:

`\begin{pmatrix}-9&1&0\\ \:4&0&2\\ \:0&1&5\end{pmatrix}\begin{pmatrix}2\\ \:-2\\ \:1\end{pmatrix}`

`\mathrm{Multiply \ the \ rows \ of \ the \ first \ matrix \ by \ the \ columns \ of \ the \ second \ matrix:}`

`\begin{aligned}&\left(\begin{array}{ccc}-9 & 1 & 0\end{array}\right)\left(\begin{array}{c}2 \\-2 \\1\end{array}\right)=(-9) \cdot 2+1 \cdot(-2)+0 \cdot 1 \\&\left(\begin{array}{ccc}4 & 0 & 2\end{array}\right)\left(\begin{array}{c}2 \\-2 \\1\end{array}\right)=4 \cdot 2+0 \cdot(-2)+2 \cdot 1 \\&\left(\begin{array}{lll}0 & 1 & 5\end{array}\right)\left(\begin{array}{c}2 \\-2 \\1\end{array}\right)=0 \cdot 2+1 \cdot(-2)+5 \cdot 1\end{aligned}`

`=\begin{pmatrix}\left(-9\right)\cdot \:2+1\cdot \left(-2\right)+0\cdot \:1\\ 4\cdot \:2+0\cdot \left(-2\right)+2\cdot \:1\\ 0\cdot \:2+1\cdot \left(-2\right)+5\cdot \:1\end{pmatrix}`

`\mathrm{Simplify\:each\:part:}`

`=\begin{pmatrix}-20\\ 10\\ 3\end{pmatrix}`

Therefore, the correct answer is B