二元函数极值

<img src="https://raw.githubusercontent.com/liangxifeng833/my_program/master/images/math/mult_weifen/two-function-jizhi-1.png" width="500" />
<img src="https://raw.githubusercontent.com/liangxifeng833/my_program/master/images/math/mult_weifen/two-function-jizhi-2.png" width="500" />
<img src="https://raw.githubusercontent.com/liangxifeng833/my_program/master/images/math/mult_weifen/two-function-jizhi-3.png" width="500" />
<img src="https://raw.githubusercontent.com/liangxifeng833/my_program/master/images/math/mult_weifen/two-function-jizhi-4.png" width="500" />
<img src="https://raw.githubusercontent.com/liangxifeng833/my_program/master/images/math/mult_weifen/two-function-jizhi-5.png" width="500" />