Answer
$a_n=40\cdot(5)^{n-1}$
Work Step by Step
The nth term of a geometric series can be obtained by the following formula: $a_n=a_1\cdot r^{n-1}$, where $a_1$ is the first term and $r$ is the common ratio.
$a_2=a_1\cdot r$, thus $a_1=40$
Here the common ratio is $r=5$ and $a_1=40$.
Hence here $a_n=40\cdot(5)^{n-1}$
