Another word for antiderivative is primitive or integral. A basic fact is that antiderivatives of functions are unique up to a constant. That means that if both F(x) and G (x) are antiderivatives of f (x), then it must be that G(x) = F(x) + C for some constant C. Wait a minute! What about F(x) = x+2 4x+3 and G(x) = -15 x-10, 4x+3 ? We compute that they are both antiderivatives of the same function h(x), where h(x) = So F(x) and G(x) must be different by a constant, and in fact that constant is F(x) - G(x) = 4