Problem 4 - Entrance Test

Using the identity (a+b)^2 = a^2 + 2ab + b^2, here a = x/2 and b = 2/x. So, (x/2 + 2/x)^2 = (x/2)^2 + 2(x/2)(2/x) + (2/x)^2 = x^2/4 + 2(1) + 4/x^2 = x^2/4 + 2 + 4/x^2.