Answer
$\begin{bmatrix} -7\sqrt {5} \\ 3 \sqrt 5 \end{bmatrix}$
Work Step by Step
$AB=\begin{bmatrix} -9 & 2 & 1 \\ 3 & 0 & 0 \end{bmatrix} \begin{bmatrix} \sqrt 5 \\ \sqrt {20} \\ - 2\sqrt 5 \end{bmatrix} \\=\begin{bmatrix} \sqrt 5(-9)+(\sqrt {20})(2)-2\sqrt 5 \\(\sqrt 5)(3)+0+0 \end{bmatrix}\\=\begin{bmatrix} \sqrt 5 (-9) +\sqrt {5} (4)-2\sqrt 5 \\ 3 \sqrt 5 \end{bmatrix}\\= \begin{bmatrix} -7\sqrt {5} \\ 3 \sqrt 5 \end{bmatrix}$
