## College Algebra (6th Edition)

Exponential growth and decay models are given by $A=A_{0}e^{kt}$ in which $t$ represents time, $A_{0}$ is the amount present at $t=0$, and $A$ is the amount present at time $t$. If $k>0$, the model describes growth and $k$ is the growth rate. If $k<0$, the model describes decay and $k$ is the decay rate. ------- So, we recognize a growth or decay model by the sign of the exponent in the exponential model.