Chapter 5 - Section 5.7 - Negative Exponents and Scientific Notation - Exercise Set - Page 409: 53

$\dfrac{1}{x^6}$

Using the laws of exponents, the given expression, $ \left( \dfrac{x^4}{x^2} \right)^{-3} ,$ simplifies to \begin{array}{l}\require{cancel} \left( x^{4-2} \right)^{-3} \\\\= \left( x^{2} \right)^{-3} \\\\= x^{2(-3)} \\\\= x^{-6} \\\\= \dfrac{1}{x^6} .\end{array}