z=4(x-y)-x^2-y^2 求极值令0=Zx=4-2x ,0=Zy=-4-2y 得到一个点(=2,-2)然后Zxx=-2 Zyy=-2 Zxy=0 K=Z^2xy-Zxx*Zxy=-4 K(2,-2)=-4 Z(2,-2)=-2,函数在(2,-2)有极大值为8这里的Zxx是对Zx的二次求导 但是Zxy是什么啊这个不懂
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![z=4(x-y)-x^2-y^2 求极值令0=Zx=4-2x ,0=Zy=-4-2y 得到一个点(=2,-2)然后Zxx=-2 Zyy=-2 Zxy=0 K=Z^2xy-Zxx*Zxy=-4 K(2,-2)=-4 Z(2,-2)=-2,函数在(2,-2)有极大值为8这里的Zxx是对Zx的二次求导 但是Zxy是什么啊这个不懂](/uploads/image/z/13945351-31-1.jpg?t=z%3D4%28x-y%29-x%5E2-y%5E2+%E6%B1%82%E6%9E%81%E5%80%BC%E4%BB%A40%3DZx%3D4-2x+%2C0%3DZy%3D-4-2y+%E5%BE%97%E5%88%B0%E4%B8%80%E4%B8%AA%E7%82%B9%EF%BC%88%3D2%2C-2%EF%BC%89%E7%84%B6%E5%90%8EZxx%3D-2+Zyy%3D-2+Zxy%3D0+K%3DZ%5E2xy-Zxx%2AZxy%3D-4+K%282%2C-2%29%3D-4+Z%282%2C-2%29%3D-2%2C%E5%87%BD%E6%95%B0%E5%9C%A8%EF%BC%882%2C-2%EF%BC%89%E6%9C%89%E6%9E%81%E5%A4%A7%E5%80%BC%E4%B8%BA8%E8%BF%99%E9%87%8C%E7%9A%84Zxx%E6%98%AF%E5%AF%B9Zx%E7%9A%84%E4%BA%8C%E6%AC%A1%E6%B1%82%E5%AF%BC+%E4%BD%86%E6%98%AFZxy%E6%98%AF%E4%BB%80%E4%B9%88%E5%95%8A%E8%BF%99%E4%B8%AA%E4%B8%8D%E6%87%82)
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