求极值就只能用导数判断了.y' = 1/2 * [ 2x*(x-1)^2 - 2(x^2 - 2)(x-1)] / (x-1)^4= 1/2 * (-2x^2 + 6x - 4) / (x-1)^4= - (x-1)(x-2) / (x-1)^4= - (x-2) / (x-1)^3当x>2时,导数是负的（注意前面有负号）,函数单调...