Compare the size of x2-xy + Y2 and X + Y-1 Step by step,

Compare the size of x2-xy + Y2 and X + Y-1 Step by step,

(x ^ 2-xy + y ^ 2) - (x + Y-1) = [(x ^ 2-2xy + y ^ 2) + (x ^ 2-2x + 1) + (y ^ 2-2y + 1)] / 2 = [(X-Y) ^ 2 + (x-1) ^ 2 + (Y-1) ^ 2] / 2 > = 0, when X-Y = X-1 = Y-1, i.e. x = y = 1, the equal sign is taken