Exponential function if a<0
I am learning about exponential function from math book for high-school.
I have learned about if and . I have understand pretty much of it, but I didn't find any explanation if (why?).
I have tried to understand by myself properties of exponential function if and .
This is what I think are properties:
1) for and function is defined but there is no inverse function
2) for and function is defined but there is inverse function
Can someone explain me a little bit about that?