Answer
$\displaystyle \frac{1-ab^{2}}{b^{2}}$
Work Step by Step
$b^{-2}-a$=.........$\displaystyle \frac{1}{a^{n}}=a^{-n}$ ........
$=\displaystyle \frac{1}{b^{2}}-a$=......... common denominator: $b^{2}$ ....
$=\displaystyle \frac{1}{b^{2}}-\frac{ab^{2}}{b^{2}}$
$= \displaystyle \frac{1-ab^{2}}{b^{2}}$
