third option.
Step-by-step explanation:
By definition we know tht the geometric sequences has a common ratio, which is represented with r.
This ratio can be calculated by dividing a term by the previous term.
Therefore, keeping the information above on mind, you have that the ratio r Β of the geometric sequence given in the problem, is the shown below:
![r=\frac{-\frac{1}{2}}{\frac{1}{10}}\\\\r=-5](/tpl/images/0360/4848/666c0.png)