Question

IF $B=\left[\begin{array}{cc}1& 3\\ -2& 5\end{array}\right]$ and $C=\left[\begin{array}{cc}-2& 5\\ 3& 4\end{array}\right]$, then find the value of $B-4C$.

Answer 1

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

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

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

$=\left[\begin{array}{cc}1& 3\\ -2& 5\end{array}\right]-\left[\begin{array}{cc}-8& 20\\ 12& 16\end{array}\right]$

$=\left[\begin{array}{cc}1-(-8)& 3-20\\ -2-12& 5-16\end{array}\right]$

$=\left[\begin{array}{cc}9& -17\\ -14& -11\end{array}\right]$