Chapter 5 - Exponents and Polynomials - 5.6 - Integral Exponents and Scientific Notation - Problem Set 5.6 - Page 224: 80

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

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