[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=-3\\
r=9
\end{cases}\implies a_n=-3(9)^{n-1}[/tex]
for a geometric sequence, the values "n" can take on for it to work, is usually all whole numbers, or positive integers, including 0, or you can say { x | x ∈ ℤ; x ⩾ 0 }
