Answer
$a_n=144\cdot(\frac{1}{3})^{n-1}$
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.
$a_3=a_1\cdot r^2$, thus $r=\frac{1}{3}$
Here the common ratio is $r=\frac{1}{3}$ and $a_1=144$.
Hence here $a_n=144\cdot(\frac{1}{3})^{n-1}$
