Answer
$y^{-5} \left( 1-3y^{2} \right)$
Work Step by Step
Factoring the given factor, $
y^{-5}
,$ then the given expression, $
y^{-5}-3y^{-3}
,$ is equivalent to
\begin{array}{l}\require{cancel}
y^{-5} \left( \dfrac{y^{-5}}{y^{-5}}-\dfrac{3y^{-3}}{y^{-5}} \right)
\\\\=
y^{-5} \left( y^{-5-(-5)}-3y^{-3-(-5)} \right)
\\\\=
y^{-5} \left( y^{-5+5}-3y^{-3+5} \right)
\\\\=
y^{-5} \left( y^{0}-3y^{2} \right)
\\\\=
y^{-5} \left( 1-3y^{2} \right)
.\end{array}
