设函数f(x,y)在(2,-2)处可微,满足f(sin(xy)+2cosx,xy-2cosy)=1+x2+y2+o(x2+y2),这里o(x2+y2)表示比x2+y2高阶的无穷小((x,y)→(0,0)时),试求曲面z=f(x,y)在点(2,-2,f(2,

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问题 设函数f(x,y)在(2,-2)处可微,满足f(sin(xy)+2cosx,xy-2cosy)=1+x2+y2+o(x2+y2),这里o(x2+y2)表示比x2+y2高阶的无穷小((x,y)→(0,0)时),试求曲面z=f(x,y)在点(2,-2,f(2,-2))处的切平面.

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答案因为f(x,y)在(2,-2)处可微,所以f(x,y)在(2,-2)处连续, 取(x,y)=(0,0)得f(2,-2)=1. 因为f(x,y)在(2,-2)处可微,所以f(x,y)在(2,-2)处可偏导, [*] [*]

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