Dividing (a+b)2+(a−b)2 by (a2+b2) gives
Given that numerator is (a+b)2+(a−b)2 = a2+b2+2ab)+(a2+b2−2ab)
= 2(a2+b2)
Hence (a+b)2+(a−b)2 by (a2+b2) = 2(a2+b2)(a2+b2)
= 2