Precalculus: Mathematics for Calculus, 7th Edition

$(a+b+2)(a+b-5)$
$(a+b)^{2}-3(a+b)-10$ Let $a+b$ be equal to $x$: If $a+b=x$, then $(a+b)^{2}=x^{2}$ Rewrite the expression using the new variable $x$: $x^{2}-3x-10=...$ Factor this expression: $...=(x+2)(x-5)=...$ Substitute $x$ back to $a+b$: $...=(a+b+2)(a+b-5)$