Answer
Geometric with a common ratio of $-1$.
Work Step by Step
Check if there is a common ratio by diving each pair of consecutive terms:
$\dfrac{1}{-1}$ $=-1$;
$\dfrac{-1}{1}$ $=-1$ ;
$\dfrac{1}{-1}$ $=-1$.
The ratio is constant so the sequence is geometric.
The common ratio is $-1$.
