Question

It is question about series topic geometric series?

Answer 1

`r = -2/7`

Explanation:

`s_oo = a/(1-r)` for `|r| < 1`

`=> (3a)/(1-r) = (a)/(1-(-2r) )`

`=> 3/(1-r) = 1/(1+2r)`

`=> 3 + 6r = 1 - r`

`=> r = -2/7`