We know that the function f (x) defined on the real number set is not always 0, and for any X. y belongs to R, satisfying XF (y) = YF (x), and judge the parity of F (x)

We know that the function f (x) defined on the real number set is not always 0, and for any X. y belongs to R, satisfying XF (y) = YF (x), and judge the parity of F (x)

f(y)=yf(x)/x
f(-y)=-yf(x)/x=-f(y)
So f (x) is an odd function