Expert: Ahmed Salami - 7/13/2004

Question
Is y=-3^x a exponential function? The reason I say it might, is:the equation for an exponential function is y=ab^x, so maybe a is a negative 1, and the b is 3.Thus, it's a exponential function because b is greater than 0 and not equal to one. Also, if I'm correct, this raises another question, why does a textbook have to say b>0,, when will it ever be? You can always say a is negative.
Thank you for your time and am looking forward to hearing back from you.

Answer
Hi Ab,
I guess b should be greater than zero because of the problem that would arise when you try to find the solution of an equation like that using logarithms. We can't find the log of a negative number.
Consider this,
-3^x = 3
How do we solve this using logs? I believe you now get the gist. You can always get back to me.
Regards.