Chapter 5 - Section 5.7 - Factoring by Special Products - Exercise Set - Page 310: 63

$\left( \dfrac{x}{5}-\dfrac{y}{3} \right)\left( \dfrac{x}{5}+\dfrac{y}{3} \right) $

Using $a^2-b^2=(a+b)(a-b)$ or the factoring of the sum of 2 squares, then, \begin{array}{l} \dfrac{x^2}{25}-\dfrac{y^2}{9} \\\\= \left( \dfrac{x}{5}-\dfrac{y}{3} \right)\left( \dfrac{x}{5}+\dfrac{y}{3} \right) .\end{array}