不正确.只可能是
limf'(x)的极限可能不存在.可以举个例子么？分段函数f(x)=2x.......x<1 x^2-x.....x>=1f'(x) =2......x<1=2x-1....x>=1limf'(x) (x->1左极限) =2limf'(x)(x->1右极限)=1而f'(1)=1