k k\,k is an integer. Prove algebraically that the expression (k−1)(k−2)+k−1(k - 1)(k - 2) + k - 1(k−1)(k−2)+k−1 is always a square number.
56 exam-style questions on Edexcel GCSE Maths Proof. Each one has a worked solution and a mark scheme showing where the marks go.