Chapter 7 - Sections 7.1-7.5 - Integrated Review - Radicals and Rational Exponents - Page 447: 38

$\dfrac{7}{\sqrt[]{21}}$

Multiplying both the numerator and the denominator by $ 7 $, then the rationalized-numerator form of the given expression, $ \sqrt[]{\dfrac{7}{3}} ,$ is \begin{array}{l}\require{cancel} \sqrt[]{\dfrac{7}{3}\cdot\dfrac{7}{7}} \\\\= \sqrt[]{\dfrac{(7)^2}{21}} \\\\= \dfrac{\sqrt[]{(7)^2}}{\sqrt[]{21}} \\\\= \dfrac{7}{\sqrt[]{21}} .\end{array}