why is graph y = 3 ^ -x ..is not onto?what is codomain?

Question

and the range for y = 4/(x^2) is R^+...why is it not R+/{0}

Answer 1

The graph is not onto because y will not equal any negative number, no matter what x you choose. The codomain is just the range of a function.

Answer 2

y=3^-x The domain are all real numbers and the codomain are all real numbers >0 ( The function is never negative nor zero)

y=4/x^2 Domain all real except 0 Codomain all positive real.