【简答题】
设函数f(x)在[0,1]上连续,在(0,1)上可导,且f(0)=f(l)=0,f(<img src="https://nimg.ppkao.com/2019-11/wangqiong/2019112916470697063.jpg?sign=1768f5a10bd3412a8dd86546a19f110e&t=62e5113a" />)=1。证明: 存在ξ∈(<img src="https://nimg.ppkao.com/2019-11/wangqiong/2019112916470697063.jpg?sign=1768f5a10bd3412a8dd86546a19f110e&t=62e5113a" />,1),使得f(ξ)=ξ:
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