求指导本题解题过程，谢谢您！33.设函数f(u)有连续一阶导数, (0)=2, 且 =xf(dfrac (y)(x))+yf(dfrac (y)(x)) 满足 dfrac (partial z)(partial x)+dfrac (partial z)(partial y)=dfrac (y)(x)-|||-(xneq 0), 求z的表达式.

求指导本题解题过程，谢谢您！