Which expression can be factorised using the identity for the difference of two squares?

Correct answer: \(a^2-b^2\)

Direct answer: A, \(a^2-b^2\). The difference-of-squares identity is \(a^2-b^2=(a-b)(a+b)\). The expression in A has two perfect-square terms, \(a^2\) and \(b^2\), joined by a minus sign, so it fits the pattern exactly. Option A therefore factors as \((a-b)(a+b)\). Option B is a three-term perfect square: \(a^2+2ab+b^2=(a+b)^2\), so it uses a different identity. Option C is a sum of squares, not a difference; the given identity cannot be applied directly. Option D is a trinomial, but its middle coefficient is 1 rather than the required 2 for the standard perfect-square pattern, and it is not the difference of two squares. Memory cue: the name itself gives the test—look for two squares separated by a minus sign.