Verify both parts of Theorem $1.16$ for the scalar, vectors, and matrix given .
$a=2, A=\left(\begin{array}{rr}-1 & 2 \\ 3 & 0\end{array}\right), \mathbf{x}=\left(\begin{array}{r}1 \\ -2\end{array}\right), \mathbf{y}=\left(\begin{array}{l}0 \\ 4\end{array}\right)$