Hi guys,

I am trying to solve the following inequality:

$\frac{a. r^n}{(1 - r)} < 10^{-5}$ where a = 2 and $r = - \frac{1}{4}$

which gives:

$(\frac{-1}{4})^n < \frac{5}{8} \times 10^{-5}$

If there were no minus sign attached to the 1 / 4, I could just take logs and solve for n, but with the - sign I am reduced to calculating $(- \frac{1}{4}) ^ n$ for successive values of n, until I get to my answer. Does anyone have a better way of doing this?

thanks