X a 2 b 2 ab 1 July 8, 2019 16 32 64 128 25x2 15 a b x 2 a b 2 ab 0 Factorise ab x 2 1 )+ x a 2 b 2 25x 2 15 a b * x 2 * a b 2 ab 0 ( a+b)2