Originally Posted by

**Plato** **Why not at least try it?**

$T\left( {\alpha \left[ {\begin{array}{*{20}{c}}x\\y\end{array}} \right]} \right) = T\left( {\left[ {\begin{array}{*{20}{c}}{\alpha x}\\{\alpha y}\end{array}} \right]} \right) = \left[ {\begin{array}{*{20}{c}}{\alpha x - 4\alpha y}\\{3\alpha x}\end{array}} \right]$

ALSO

${T^2}\left( {\left[ {\begin{array}{*{20}{c}}

x\\

y

\end{array}} \right]} \right) = T \circ T\left( {\left[ {\begin{array}{*{20}{c}}

x\\

y

\end{array}} \right]} \right) = \left[ {\begin{array}{*{20}{c}}

{(x - 4y) - 12x}\\

{3x - 12y}

\end{array}} \right]$ **WHY & HOW?**

Post your work so others may see .