# How do you find nth term rule for -28,14,-7,7/2,-7/4,...?

Aug 17, 2016

${a}_{n} = - 28 {\left(- \frac{1}{2}\right)}^{n - 1}$

#### Explanation:

$\frac{- 7}{14} = - \frac{1}{2} \text{ and } \frac{14}{- 28} = - \frac{1}{2}$

It is a GP with ${a}_{1} = - 28$ and Common ratio = $r = - \frac{1}{2}$

${a}_{n} = a {r}^{n - 1}$

${a}_{n} = - 28 {\left(- \frac{1}{2}\right)}^{n - 1}$