A common ratio is basically a ratio of next sequence and the sequence you want
To find a common ratio of geometric sequence, we usually define 'r' as common ratio.
![\displaystyle \large \tt{r = (next \: \: sequence)/(the \: \: sequence \: \: you \: \: want) }](https://img.qammunity.org/2022/formulas/mathematics/high-school/ilwbrcvxw7xkubdsk7555zvmayavl2ow5r.png)
For example, I want to focus on -14 and the next sequence would be -84.
Hence,
![\displaystyle \large{r = ( - 84)/( - 14) }](https://img.qammunity.org/2022/formulas/mathematics/high-school/iwlrdq2y3b1p684yfi4i5w94dgkalum88j.png)
Thus, r is 6 because both numerator and denominator are negative. negative divides negative = positive.
Or you want to choose -84, then the next sequence would be -504.
![\displaystyle \large{r = ( - 504)/( - 84) }](https://img.qammunity.org/2022/formulas/mathematics/high-school/pvnif4vql3hjewbt6c6auwtaquz88oa85l.png)
Then r would still be 6. Since both ways have r as 6 and this proves that the sequence is geometric.
Hence, the common ratio is 6.