f'(x)＞0 =＞ f(x)增f'(x)＜0 => f(x)减这个是充分不必要条件在区间A中f'(x)≥0且对A的任意一个子区间f'(x)不恒为零<=>f(x)在区间A单调增。同理可以写出单调减的充要条件
