函数<img src="https://static.zxtiku.com/wangke/imgs/topic/2d716dc78fbb762de3db96a12b73d156.png"/>在点<img src="https://static.zxtiku.com/wangke/imgs/topic/25600749ca3651baa80c47fd29487609.png"/>处沿方向<img src="https://static.zxtiku.com/wangke/imgs/topic/bf5a72a4d2b387e24cd66d10bc2194fb.png"/>的方向导数为2