Answer
$\frac{-1}{2},\frac{1}{4},\frac{-1}{8},\frac{1}{16}$
Work Step by Step
$a_n = \frac{(-1)^n}{2^n}$
To find the first four terms, we need to find $a_1, a_2, a_3$, and $a_4$.
$a_1 = \frac{(-1)^1}{2^1} = \frac{-1}{2}$
$a_2= \frac{(-1)^2}{2^2} = \frac{1}{4}$
$a_3 = \frac{(-1)^3}{2^3} = \frac{-1}{8}$
$a_4 = \frac{(-1)^4}{2^4} = \frac{1}{16}$
