$\left[\begin{array}{cc}5 & -1 \\ 6 & 7\end{array}\right]\left[\begin{array}{ll}2 & 1 \\ 3 & 4\end{array}\right]$

$=\left[\begin{array}{ll}5(2)-1(3) & 5(1)-1(4) \\ 6(2)+7(3) & 6(1)+7(4)\end{array}\right]$

$=\left[\begin{array}{cc}10-3 & 5-4 \\ 12+21 & 6+28\end{array}\right]$ $=\left[\begin{array}{cc}7 & 1 \\ 33 & 34\end{array}\right]$

$\left[\begin{array}{ll}2 & 1 \\ 3 & 4\end{array}\right]\left[\begin{array}{ll}5 & -1 \\ 6 & 7\end{array}\right]$

$=\left[\begin{array}{ll}2(5)+1(6) & 2(-1)+1(7) \\ 3(5)+4(6) & 3(-1)+4(7)\end{array}\right]$

$=\left[\begin{array}{cc}10+6 & -2+7 \\ 15+24 & -3+28\end{array}\right]=\left[\begin{array}{cc}16 & 5 \\ 39 & 25\end{array}\right]$

$\therefore  $ $\left[ {\begin{array}{*{20}{c}}
  5&{ – 1} \\ 
  6&7 
\end{array}} \right]\left[ {\begin{array}{*{20}{l}}
  2&1 \\ 
  3&4 
\end{array}} \right]$ $ \ne \left[ {\begin{array}{*{20}{l}}
  2&1 \\ 
  3&4 
\end{array}} \right]\left[ {\begin{array}{*{20}{l}}
  5&{ – 1} \\ 
  6&7 
\end{array}} \right]$