a^2-b^2=(a+b)(a-b) is the most tested factoring pattern on the examination, and it is tested disguised: 4x^2-9=(2x+3)(2x-3); x^4-16=(x^2+4)(x+2)(x-2) — students routinely stop short of the second factoring; and x^2-5=(x+sqrt5)(x-sqrt5), since nothing requires b to be an integer. There is no sum-of-squares factoring over the reals, and the examination offers one as a distractor.