Chapter 5 - Exponents and Polynomials - 5.6 - Integral Exponents and Scientific Notation - Problem Set 5.6 - Page 223: 14

$\dfrac{1}{9}$

Using $a^{-x}=\dfrac{1}{a^x}$ or $\dfrac{1}{a^{-x}}=a^x$ and the laws of exponents, the given expression, $ \left( -3 \right)^{-2} ,$ is equivalent to \begin{array}{l}\require{cancel} \dfrac{1}{(-3)^2} \\\\= \dfrac{1}{9} .\end{array}