(ƒ+g)(x) ƒ(x) = x+3, g(x) = x - 3
(ƒ+g)(x), ƒ(x) = x+3, g(x) = x - 3
(ƒ+g)(x) = f(x) + g(x) = (x + 3) + (x - 3) = 2x