程x2+2y2+z2-4yz+2z+3=0两端x求偏导2x+2z?zx-4y?zx+2zx=0即zx=x2y?z?1两端y求偏导4y+2z?zy-4z-4y?zy+2?zy=0即zy=2y?2z2y?z?1令zx=zy=0解:x=0y=zx=0y=z代入已知程解y=z=-1或者y=z=3即隐函数z=z(xy)两驻点:(0-1)、(03)A=zxx=(2y?z?1)?x(?zx)(2y?z?1)2B=zxy=?x(2?zy)(2y?z?1)2C=zyy=2(2y?z?1)?(y?z)(2?zy)(2y?z?1)2(0-1-1)代入求:A=?12B=0C=-1AC?B2=12>0且A<0隐函数z=z(xy):(0-1)取极值(033)代入求:A=12B=0C=1AC?B2=12>0且A>0隐函数z=z(xy):(03)取极值
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