a^2 + ab + b^2 = 1(a + b)^2 = a^2 + 2ab + b^2 = a^2 + ab + b^2 + ab = 1 + ab >= 0ab >= -1(a - b)^2 = a^2 - 2ab + b^2 = a^2 + ab + b^2 - 3ab = 1 - 3ab >= 0ab