Find the First Term a_n=(-2)^(n-1)

$a_{n} = {(- 2)}^{n - 1}$

Substitute in the value of $n$ to find the $n$ th term.

$a_{1} = {(- 2)}^{(1) - 1}$

Subtract $1$ from $1$ .

$a_{1} = {(- 2)}^{0}$

Anything raised to $0$ is $1$ .

$a_{1} = 1$