Chapter 5 - Polynomials and Factoring - 5.4 Factoring Perfect-Square Trinomials and Differences of Squares - 5.4 Exercise Set - Page 333: 97

$6x^4+x^2y-y^2$

Using $(a+b)(c+d)=ac+ad+bc+bd$ or the product of $2$ binomials, the given expression, $ (2x^2+y)(3x^2-y) ,$ simplifies to \begin{array}{l} 2x^2(3x^2)+2x^2(-y)+y(3x^2)+y(-y) \\\\= 6x^4-2x^2y+3x^2y-y^2 \\\\= 6x^4+x^2y-y^2 \end{array}