What is the simplified form of \( (x+a)(x-a)(x^2+a^2) \)?

Correct answer: \(x^4-a^4\)

First use the identity \((x+a)(x-a)=x^2-a^2\). The expression becomes \((x^2-a^2)(x^2+a^2)\). Applying \((p-q)(p+q)=p^2-q^2\), with \(p=x^2\) and \(q=a^2\), gives \(x^4-a^4\). Option D is the expansion of \((x^2-a^2)^2\), so it is not applicable here. Exam tip: identify conjugate factors step by step and use the difference-of-squares identity.