▶点拨 (a)f'(x)>0(或f'(x)<0)是f(x)在(a,b)内单调递增(或递减)的充分不必要条件. (b)f'(x)=0不恒成立时,f'(x)≥0(或f'(x)≤0)是可导函数f(x)在(a,b)内单调递增(或递减)的充要条件.