若函数<img src="https://static.zxtiku.com/wangke/imgs/topic/c924f1429a5ced00951aca28d7090b87.png"/>在<img src="https://static.zxtiku.com/wangke/imgs/topic/ddbc0258523ac7132fd0ba42d9b6228b.png"/>处连续，则函数<img src="https://static.zxtiku.com/wangke/imgs/topic/c8a8a29c813592f70142c47faaa73fd4.png"/>在<img src="https://static.zxtiku.com/wangke/imgs/topic/ddbc0258523ac7132fd0ba42d9b6228b.png"/>处可导当且仅当<img src="https://static.zxtiku.com/wangke/imgs/topic/ef44422f12a3ce1785ae4b480f81f04a.png"/>．‌