设<img src="https://static.zxtiku.com/wangke/imgs/topic/9b311369aff8c9d4d11a743d296cb308.png"/> 是可导函数且<img src="https://static.zxtiku.com/wangke/imgs/topic/d8609d1dd682ddfbe6a8642362958890.png"/> ,则曲线<img src="https://static.zxtiku.com/wangke/imgs/topic/8a28911fd762586ae2a02ce9792941d4.png"/> 在<img src="https://static.zxtiku.com/wangke/imgs/topic/e9a6e11453fbdf36ee3f8d57210e0f9e.png"/> 处的切线斜率为( ).