## College Algebra (10th Edition)

$a_n=(-1)^{n+1}$
The pattern involves alternating signs of for the number $1$. This means that the pattern's formula involves a power of $-1$. Since the first term is positive, the exponent in the sequence's formula could involve either $n+1$ or $n-1$. If the exponent $n+1$ is used, then the formula for the $n^{th}$ term of the sequence is: $a_n=(-1)^{n+1}$