to find the common ratio on any geometric sequence we can simply grab two consecutive terms and divide the second by the first one, in essence dividing the later by the previous term, give us the common ratio. So let's do that in this case hmmm say let's divide the last two terms here
![\cfrac{49}{3}/ \cfrac{-7}{3}\implies \cfrac{49}{3}\cdot -\cfrac{3}{-7}\implies -7\leftarrow \textit{common ratio} \\\\[-0.35em] ~\dotfill\\\\ a_1=-\cfrac{1}{21}\hspace{5em}a_n=a_(n-1)(-7)](https://img.qammunity.org/2024/formulas/mathematics/college/mxw1i1kjb1z31jns14k0nzxt8cbfki5eqv.png)