‎<img src="https://static.zxtiku.com/wangke/imgs/topic/a83daaaa89c26b04b76ca47594b21078.png"/>在点<img src="https://static.zxtiku.com/wangke/imgs/topic/591ec9aff39ac2e8842bdcc7931b14e2.png"/>处可导的充要条件是函数<img src="https://static.zxtiku.com/wangke/imgs/topic/3ef1766752502f7ede8713ad058e82ae.png"/>，<img src="https://static.zxtiku.com/wangke/imgs/topic/96bfda1ed186e2469e91ab1f03a5a34c.png"/>与<img src="https://static.zxtiku.com/wangke/imgs/topic/48e70b3f131945bd0e52d2a95b2a13c1.png"/>在<img src="https://static.zxtiku.com/wangke/imgs/topic/591ec9aff39ac2e8842bdcc7931b14e2.png"/>处都可导.‏