Answer
$a_n=1\times(-1)^{n-1}=(-1)^{n-1}$
Work Step by Step
The general term in a geometric sequence is:
$a_n=a_1\times r^{n-1}$
Here, $a_1=1$
We can find the common ratio by dividing two subsequent terms:
$r=\frac{a_2}{a_1}=\frac{-1}{1}=-1$
The general term is:
$a_n=1\times(-1)^{n-1}=(-1)^{n-1}$
