Answer
$-\dfrac{1}{549, 755, 813.888}$
Work Step by Step
The general formula to find the nth term of a Geometric sequence is given as: $ a_{n}=a_1r^{n-1}$
We are given that $ a_1=1000, r=-\dfrac{1}{2}; n=40$
Now, $ a_{40}=1000 \times (-\dfrac{1}{2})^{40-1}=1000 (-\dfrac{1}{2})^{39}$
$\implies a_{40}=-\dfrac{1}{549, 755, 813.888}$
