f(x+y-xy)+f(xy)=f(x)+f(y)

Solution for f(x+y-xy)+f(xy)=f(x)+f(y) equation:

Simplifying
f(x + y + -1xy) + f(xy) = f(x) + f(y)

Reorder the terms:
f(x + -1xy + y) + f(xy) = f(x) + f(y)
(x * f + -1xy * f + y * f) + f(xy) = f(x) + f(y)
(fx + -1fxy + fy) + f(xy) = f(x) + f(y)

Multiply f * xy
fx + -1fxy + fy + fxy = f(x) + f(y)

Reorder the terms:
fx + -1fxy + fxy + fy = f(x) + f(y)

Combine like terms: -1fxy + fxy = 0
fx + 0 + fy = f(x) + f(y)
fx + fy = f(x) + f(y)

Multiply f * x
fx + fy = fx + f(y)

Multiply f * y
fx + fy = fx + fy

Add '-1fx' to each side of the equation.
fx + -1fx + fy = fx + -1fx + fy

Combine like terms: fx + -1fx = 0
0 + fy = fx + -1fx + fy
fy = fx + -1fx + fy

Combine like terms: fx + -1fx = 0
fy = 0 + fy
fy = fy

Add '-1fy' to each side of the equation.
fy + -1fy = fy + -1fy

Combine like terms: fy + -1fy = 0
0 = fy + -1fy

Combine like terms: fy + -1fy = 0
0 = 0

Solving
0 = 0

Couldn't find a variable to solve for.

This equation is an identity, all real numbers are solutions.