Take two numbers whose sum is 1. Which do you think is larger: the square of the smaller added to the larger or the square of the larger added to the smaller? Why?
Consider x and 1 – x, with x the larger.
x + (1 – x)2 = x + 1 – 2x + x2 = 1 – x + x2
(1 – x) + x2 = 1 – x + x2.
They’re the same.