Chapter 5 - Section 5.4 - Multiplying Polynomials - Exercise Set - Page 289: 45

$x^4-2x^2y^2+y^4$

Using special products, the given expression is equivalent to \begin{align*} & (x+y)(x-y)(x^2-y^2) \\\\&= (x^2-y^2)(x^2-y^2) \\\\&= (x^2-y^2)^2 \\\\&= (x^2)^2+2(x^2)(-y^2)+(-y^2)^2 \\\\&= x^4-2x^2y^2+y^4 .\end{align*}