Chapter 10 - Exponents and Radicals - 10.2 Rational Numbers as Exponents - 10.2 Exercise Set - Page 641: 91

$\sqrt{7a}$

Using $a^{m/n}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m$, the given expression, $ \sqrt[4]{(7a)^2} ,$ is equivalent to \begin{array}{l}\require{cancel} (7a)^{2/4} \\\\= (7a)^{1/2} \\\\= \sqrt{(7a)^1} \\\\= \sqrt{7a} .\end{array}