若f(x,y)=x^2-y^2,则f(x+y,y/x)=(x+y)^2-(y/x)^2 若f(x+y,y/x)=x^2-y^2令a=x+y , b=y/x则y=bx, a=x+bx, 得:x=a/(1+b),y=ab/(1+b)故f(a, b)=a^2/(1+b)^2 -(ab)^2/(1+b)^2=a^2/(1+b)^2*(1-b^2)=a^2(1-b)/(1+b)即f(x, y)=x^2(1-y)/(1+y)望采纳 O(∩_∩)O谢谢