Precalculus: Mathematics for Calculus, 7th Edition

$(1+x)(2-x)-(3-x)(3+x)=x-7$
$(1+x)(2-x)-(3-x)(3+x)$ Evaluate both products and simplify: $(1+x)(2-x)-(3-x)(3+x)=...$ $...=(2-x+2x-x^{2})-(9-x^{2})=...$ $...=-x^{2}+x+2+x^{2}-9=...$ $...=x-7$