f(x)f(y) = f(x+y) + xy
I need to find all possible functions f
I have tried some substitutions such as x = y = 0
f(0)f(0) = f(0) + 0
so f(0) = 0 or f(0) = 1
Then let x = 0
f(0)f(y) = f(y)
I think this implies that f(0) has to be 1.
Not sure where to go from here.
