Let f1(x) and f2(x) be functions from the set of real numbers to the set of positive real numbers. Show that if f1(x) and f2(x) are both (g(x)), where g(x) is a function from the set of real numbers to the set of positive real numbers, then f1(x) + f2(x) is (g(x)). Is this still true if f1(x) and f2(x) can take negative values?