若f(x+y,x-y)=x2-y2,则f(x,y)=,
问题描述：
若f(x+y,x-y)=x2-y2,则f(x,y)=,
答
f(x+y,x-y)=x^2-y^2=(x+y)(x-y)
令x+y=a,x-y=b
那么f(a,b)=ab
所以f(x,y)=xy