Exponential growth form can be represented mathematically by the following exponential equation:
$\frac{d N}{d t}=(\mathrm{B}-\mathrm{D}) \times \mathrm{N}$
$\mathrm{B}=$ Birth rate, $\mathrm{D}=$ Death rate
Let $(B-D)=r$ or intrinsic rate of growth.
Then, $=r \times n$
where $d$ is the rate of change, $\mathrm{N}=$ number of existing individuals.
$t=$ time and $r=$ intrinsic rate of natural increase represents the rate of change in population size.