# Chapter R - Elementary Algebra Review - R.4 Polynomials - R.4 Exercise Set - Page 961: 9

$\dfrac{1}{a^2b^{2}}$

#### Work Step by Step

Using $a^{-n}=\dfrac{1}{a^n}$, the given expression, $(ab)^{-2} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{1}{(ab)^{2}} \\\\= \dfrac{1}{a^2b^{2}} .\end{array}

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