Function defined with condition in CAS
If i have a function f(x):=a*x^3-a*x in CAS, can I make it treat a as greater than zero only?
In my case I want to check wether the derivative on any x value is positive or not.
For example, f'(-2) gives 11a. Since I only want a>0, I can tell that this would be positive. Is there any way I could make CAS recognize that?