Exponential growth/decay equations & usage

In my book I am given the equation A(t) = Aoe^(kt) (for exponential growth) Where t equals time and k is a constant. However, I saw an equation on another site for compounded interest in which k was replaced by r, the rate of interest. When do you use which equation? And what about exponential decay?

Re: Exponential growth/decay equations & usage

From your description I would say that both equations are identical. They've merely applied a different nametag to the constant.

If then there is exponential growth. If there is exponential decay (towards zero).

Re: Exponential growth/decay equations & usage