设函数f(x+y，y/x)=x2-y2，求f(x，y)．

设函数f(x+y，y/x)=x2-y2，求f(x，y)．
【正确答案】：设x+y=t，y/x=υ 则f(t,υ)=[t/(1+υ)]2-[tυ/(1+υ)]2∴f(x,y)=x2[(1-x)/(1+y)]