求函数Z=xln(x+y)的二阶偏导数

问题描述:

求函数Z=xln(x+y)的二阶偏导数

二阶偏导数有四个Z''xx=(lin(x+y)+x/(x+y))'=1/(x+y)+y/(x+y)^2
Z''yy=(x/(x+y))'=-x/(x+y)^2
Z''yx=Z''xy=(x/(x+y))'x=y/(x+y)^2