If f(x+y,x−y)=xy then the arithmetic mean of f(x,y) and f(y,x) is
x
y
0
xy
Let x + y = p, x - y = q. Then
f(p,q)=p+q2⋅p−q2=p2−q24
∴ f(x,y)=x2−y24 and f(y,x)=y2−x24
A.M.=f(x,y)+f(y,x)2=0