As follows:
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(http://i707.photobucket.com/albums/ww74/stevieg90/03-125.jpg)
Hard Maths 2
2010-11-02 6:11 pm
回答 (1)
2010-11-02 7:52 pm
✔ 最佳答案
u=(p+q)/(q-r)=-2x/(x+y)= -2+ 2y/(x+y)∂u/∂x=-2y/(x+y)^2
∂u/∂y=2x/(x+y)^2
(∂/∂x)^2 u= 4y/(x+y)^3
(∂/∂y)^2 u= -4x/(x+y)^3
(∂/∂x)^2 u+(∂/∂y)^2 u =-4(x-y)/(x+y)^3 =0, then x=y(≠0)
so, u=-2x/(x+y)= -1
收錄日期: 2021-04-22 00:58:50
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20101102000051KK00287