Prove that (n+3)2−(n−3)2(n + 3)^2 - (n - 3)^2(n+3)2−(n−3)2 is always a multiple of 12, for all positive integer values of nnn.
207 exam-style questions on OCR GCSE Maths Proof. Each one has a worked solution and a mark scheme showing where the marks go.