Answer
$y(y^{2}+4)(y-2)(y+2)$
Work Step by Step
$ y^{5}-16y\qquad$...factor out the common term, $y$
$=y(y^{4}-16)\qquad$...recognize the difference of two squares: $a^{2}-b^{2}=(a-b)(a+b)$
$=y(y^{2}+4)(y^{2}-4)\qquad$...recognize the difference of two squares: $a^{2}-b^{2}=(a-b)(a+b)$
$=y(y^{2}+4)(y-2)(y+2)$
