factoring

factoring 5y^2-80

$\begin{array}{|rcll|} \hline && 5y^2-80 \\ &=& 5y^2-4^2\cdot 5 \\ &=& 5\cdot(y^2-4^2) \\ &=& 5\cdot(y-4)\cdot (y+4) \\ \hline \end{array}$