设<img src=https://huaweicloudobs.ahjxjy.cn/EA6FB79FF8DF7A9F3A2D0CEB093C717F.png title=QQ图片20160224214006.png alt=QQ图片20160224214006.png/>在<img src=https://huaweicloudobs.ahjxjy.cn/DF3DA077C2189146990B3800DA1E18ED.png title=QQ图片20160224214023.png alt=QQ图片20160224214023.png/>的偏导数存在,则<img src=https://huaweicloudobs.ahjxjy.cn/61AF63E59A60D6B49960C25A0B85414F.png title=QQ图片20160224214038.png alt=QQ图片20160224214038.png/>
①
<img src=https://huaweicloudobs.ahjxjy.cn/588DCE737E539AFE5318232DBC0C8858.png title=QQ图片20160224214107.png alt=QQ图片20160224214107.png/>
②
<img src=https://huaweicloudobs.ahjxjy.cn/1898B210FBB62DA4DA7997BB95A4D586.png title=QQ图片20160224214125.png alt=QQ图片20160224214125.png/>
③
<img src=https://huaweicloudobs.ahjxjy.cn/C9D08ECB097A69F4F22594D120D687E7.png title=QQ图片20160224214140.png alt=QQ图片20160224214140.png/>
④
<img src=https://huaweicloudobs.ahjxjy.cn/6101D759594C1C2892D8E9F8195520C5.png title=QQ图片20160224215328.png alt=QQ图片20160224215328.png/>