Elementary Algebra

$75x^3-147x$
Using $(a-b)(a+b)=a^2-b^2$, or the product of the sum and difference of like terms, the given expression, $3x(5x+7)(5x-7) ,$ is equivalent to \begin{array}{l}\require{cancel} 3x[(5x)^2-(7)^2] \\\\= 3x(25x^2-49) .\end{array} Using the Distributive Property, the expression, $3x(25x^2-49) ,$ is equivalent to \begin{array}{l}\require{cancel} 75x^3-147x .\end{array}