1) Factorise: a^2 - b^2 - 3a -3b
I keep getting stuck at (a+b)(a-b)-3(a+b), since on the answer sheet, it tells me that from that step, the final answer is (a+b)(a-b)(a-b-3). I don't understand. ;_; Help please? It's a two mark question.
2) If you have 18^(4-n), for example, can you break...