## Precalculus: Mathematics for Calculus, 7th Edition

4$x^2$ + 4xy + $y^2$ - 9
If 2x + y is considered as a single term, then this expression is equivalent to the product of the sum and difference of two terms. For any two terms, A and B, if the expression is (A + B)(A - B), then the product is equivalent to $A^2$ - $B^2$. Therefore: (2x + y - 3)(2x + y + 3) = $(2x + y)^2$ - $3^2$ $(2x + y)^2$ - $3^2$ = 4$x^2$ + 4xy + $y^2$ - 9