# Thread: Find A-2B

1. ## Find A-2B

A= 5 1 B= -1 3
3 2 4 1 Find A-2B
My answer is -1 3
4 1 I don't think this is right after using excel, thanks for checking.

2. Originally Posted by kwtolley
A= 5 1 B= -1 3
3 2 4 1 Find A-2B
My answer is -1 3
4 1 I don't think this is right after using excel, thanks for checking.
$
A=
\left[ \begin{array}{cc}
{5}& {1}\\
{3}& {2}
\end{array} \right],\ B=
\left[ \begin{array}{cc}
{-1}& {3}\\
{4}& {1}
\end{array} \right].
$

so:

$
A-2B=
\left[ \begin{array}{cc}
{5}& {1}\\
{3}& {2}
\end{array} \right]-
2 \times
\left[ \begin{array}{cc}
{-1}& {3}\\
{4}& {1}
\end{array} \right]
$

$
=
\left[ \begin{array}{cc}
{5}& {1}\\
{3}& {2}
\end{array} \right]-
\left[ \begin{array}{cc}
{-2}& {6}\\
{8}& {2}
\end{array} \right]=
\left[ \begin{array}{cc}
{7}& {-5}\\
{-5}& {0}
\end{array} \right]
$

3. ## thanks

I thought mt answer was wrong. thanks again