Question

Suppose that functions f1,f2,g1,g2: N -> R ^ > 0, natural real numbers greater than 0.
Prove that (f1 + f2) ∊ Θ(max{g1,g2}).
(f1+f2)(n) = f1(n)+f2(n) and max{g1,g2}(n) = max{g1(n) + g2(n)}