Answer
$y(y^{2}+9)(y+3)(y-3)$
Work Step by Step
$y^{5}-81y=$
Factor out the GCF, $y$
$=y(y^{4}-81)$
The parentheses hold a difference of squares,
$=y[(y^{2})^{2}-9^{2})$
$=y(y^{2}+9)(y^{2}-9)$
The last parentheses hold a difference of squares,
$=y(y^{2}+9)(y+3)(y-3)$
