求Z=X-Y/X+Y的二阶偏导数 麻烦图片回答 谢谢
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发布时间：2022-06-01 22:10
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热心网友
时间：2023-10-18 16:12
z'<x>=[1*(x+y)-(x-y)*1]/(x+y)^2=2y/(x+y)^2,
z'<y>=[-(x+y)-(x-y)*1]/(x+y)^2=-2x/(x+y)^2,
z''<xx>=2y(-2)/(x+y)^3=-4y/(x+y)^3,
z''<xy>=2{[(x+y)^2-y*2(x+y)]/(x+y)^4}=2(x-y)/(x+y)^3
z''<yy>=-2x(-2)/(x+y)^3=4x/(x+y)^3.
