## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$a(b^2+9a^2)(b+3a)(b-3a)$
Factoring the $GCF= a$, then the given expression, $b^4a-81a^5$ is equivalent to \begin{array}{l} a(b^4-81a^4) .\end{array} Using $a^2-b^2=(a+b)(a-b)$ or the factoring of the difference of $2$ squares, then the factored form of the given expression, $a(b^4-81a^4)$, is \begin{array}{l} a(b^2+9a^2)(b^2-9a^2) \\\\= a(b^2+9a^2)(b+3a)(b-3a) .\end{array}