‌设函数<img src="https://static.zxtiku.com/wangke/imgs/topic/41e7fccbe750d38bc0feb89ce7f5fb20.png"/>，则<img src="https://static.zxtiku.com/wangke/imgs/topic/bad4812492d2eb39917ad1328ab00fdf.png"/>在<img src="https://static.zxtiku.com/wangke/imgs/topic/dec489fe63c572e4c2b40e49ce9a1240.png"/>处可导。‍