若函数<img src="https://storage.tutusouti.com/psst/files/5b9ea690a6a74e5f9d187270c4912597.jpeg?x-oss-process=image/sharpen,200"/>在闭区域<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/56de753172aa4feca978fede78e4b859.png?x-oss-process=image/sharpen,200"/>上连续且有连续一阶偏导数，则有<img src="https://storage.tutusouti.com/psst/files/854efacad857434aa90e36deca8e840d.jpeg?x-oss-process=image/sharpen,200"/><br/> 这里<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/ba8d6da709e34707b8f2ceaff0fe661c.png?x-oss-process=image/sharpen,200"/>为区域<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/56de753172aa4feca978fede78e4b859.png?x-oss-process=image/sharpen,200"/>的边界曲线，分段光滑，并取负方向。