Prove that (5k+2)2−(5k−2)2(5k + 2)^2 - (5k - 2)^2(5k+2)2−(5k−2)2 is always a multiple of 40, for all positive integer values of kkk.
Practise OCR GCSE Maths Proof with exam-style questions for Foundation and Higher tier. 56 questions, matched to the OCR GCSE Maths (J560) specification and written in the written papers style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.