1. The problem statement, all variables and given/known data By expanding (x-y)^2, prove that x^2 +y^2 ≥ 2xy for all real numbers x & y. 2. Relevant equations 3. The attempt at a solution expanding (x-y)^2 x^2 - 2xy + y^2= 0 Hence, x^2 + y^2 = 2xy But where does the ≥ come into it? and why? when you put values in (except i which is not real of course) they all come out as = 2xy, which does satisfy ≥2xy, but why does this come into it?? Some insight would be fantastic!