let's recall that the common ratio is just the number we multiply the current value to get the next value in the sequence.
[tex]n^{th}\textit{ term of a geometric sequence}\\\\a_n=a_1\cdot r^{n-1}\qquad\begin{cases}a_n=n^{th}\ term\\n=\textit{term position}\\a_1=\textit{first term}\\r=\textit{common ratio}\end{cases}\\\\[-0.35em]~\dotfill\\\\\begin{array}{llll}a_1&a_2&a_3&...\\4&\underset{4\cdot 2}{8}&\underset{8\cdot 2}{16}&...\end{array}\qquad \qquad \begin{cases}a_1=4\\r=2\end{cases}[/tex]
