Chapter 6 - Factoring, Solving Equations, and Problem Solving - 6.2 - Factoring the Difference of Two Squares - Problem Set 6.2 - Page 248: 19

$x(x+5)(x-5)$

Factoring out the greatest common factor of x, the given expression, $ x^3-25x ,$ is equivalent to \begin{array}{l}\require{cancel} x(x^2-25) .\end{array} Using $a^2-b^2=(a+b)(a-b)$, the completely factored form of the expression above is \begin{array}{l}\require{cancel} x(x+5)(x-5) .\end{array}