Chapter 4 - Polynomials - 4.6 Special Products - 4.6 Exercise Set - Page 277: 76

$36x^8-36x^5+9x^2$

Using $(a+b)^2=a^2+2ab+b^2$ or the square of a binomial, the given expression, $ \left( 6x^4-3x \right)^2 $, is equivalent to \begin{array}{l}\require{cancel} (6x^4)^2+2(6x^4)(-3x)+(-3x)^2 \\\\= 36x^8-36x^5+9x^2 .\end{array}