https://web2.0calc.com/questions/help-please_89887
Written clearly in the answer.
Guest said, see if f(x) = x works.
It means, see if f(x) = x is a valid solution.
Okay, but how does that help? Let's say f(x)=x
Then, x*f(y)=f(x+y)+f(x)*y
+1005 
