Answer
See below.
Work Step by Step
$n=1:\frac{(-1)^1}{3^1-1}=\frac{-1}{3-1}=\frac{-1}{2}$
$n=2:\frac{(-1)^2}{3^2-1}=\frac{1}{9-1}=\frac{1}{8}$
$n=3:\frac{(-1)^3}{3^3-1}=\frac{-1}{27-1}=\frac{-1}{26}$
$n=4:\frac{(-1)^4}{3^4-1}=\frac{1}{81-1}=\frac{1}{80}$
