# Chapter 5 - Section 5.7 - Negative Exponents and Scientific Notation - Exercise Set - Page 408: 2

$\dfrac{1}{81}$

#### Work Step by Step

Using $x^{-a}=\dfrac{1}{x^a}$the given expression, $9^{-2} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{1}{9^2} \\\\= \dfrac{1}{81} .\end{array}

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