Chapter 5 - Section 5.4 - Multiplying Polynomials - Exercise Set - Page 289: 46

$z^4-2z^2y^2+y^4$

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