[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}\\
----------\\
n=9\\
a_1=1\\
r=-\frac{1}{3}
\end{cases}\implies a_9=1\left( -\frac{1}{3} \right)^{9-1}[/tex]
