[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=-10\\
r=2\\
n=8
\end{cases}
\\\\\\
a_8=-10\cdot 2^{8-1}\implies a_8=-10\cdot 2^7
\\\\\\
a_8=-10\cdot 128\implies a_8=-1280[/tex]
