How to prove it? I've watched a tv program before and I vaguely remember the proof consists of 4 parts, which includes the mean value theorem, Cauchy's mean value theorem and the other 2 theorems. I haven't learnt mean value theorem at that time and I didn't understand it, perhaps I can now.(adsbygoogle = window.adsbygoogle || []).push({});

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# L'hospital's rule

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