recall that in a geometric sequence, you multiply the "current" one by the common ratio to get the "next" so, if you divide "next"/"current", the quotient is just the common ratio,
![\bf \cfrac{27}{243}=\cfrac{3}{27}=\cfrac{(1)/(3)}{3}=\cfrac{(1)/(27)}{(1)/(3)}\implies \cfrac{1}{9}\impliedby \textit{common ratio}](https://img.qammunity.org/2019/formulas/mathematics/high-school/h9qs2hfh9pxfwz3l486xfc96x9lipbw0mg.png)
notice, all we did was, divide the value, by the number to its left-hand-side.