上式 = (x^2 + xy + y^2 /4) + 3*(y^2 /4 - y + 1) = (x + y/2)^2 + 3 * (y/2 - 1)^2 = 0只有当：x + y/2 = 0，y/2 - 1 = 0 时上式才能成立。即：y = 2, x = -1
