导数与函数最值问题的交汇设y=f(x)为可导函数,则“函数f(x)在某点取得极值”的充要条件是“该点的导数为零或不存在且该点两侧的导数异号”.定义在闭区间上的初等函数必存在最值,且最值只能在区间的端点或区 The intersection of the derivative and the most significant problem in the function Let y = f (x) be the function of the defulable function, then the necessary and sufficient condition for the function f (x) to obtain the extreme value at some point is that “the derivative at this point is zero or Does not exist and the derivative of the derivative on both sides of the point ”. The elementary functions defined in the closed interval must have the most value, and the maximum value only in the end of the interval or area