[tex]\bf n^{th}\textit{ term of a geometric sequence}\\\\
a_n=a_1\cdot r^{n-1}\qquad
\begin{cases}
n=n^{th}\ term\\
a_1=\textit{first term's value}\\
r=\textit{common ratio}\\
----------\\
a_1=30\\
r=\frac{1}{2}\\
n=4
\end{cases}\implies a_4=30\left( \frac{1}{2} \right)^{4-1}[/tex]
