Answer
$a_{40}=-1.819 \times 10^{-9}$
Work Step by Step
The nth term of a geometric sequence can be found using the formula:
$a_n=a_1(r^{n-1})$
where
r= common ratio
$a_1$ = first term
$a_n$ = nth term
n = term number
Substitute the given values of $a_1$, n, and $r$ to find:
$a_{40}=1000(-\frac{1}{2})^{40-1}
\\a_{40}=1000(-\frac{1}{2})^{39}
\\a_{40}=-1.818989404 \times 10^{-9}$
