Final answer:
The value of a in the geometric series -2, 4, -8, ... is 8.
Step-by-step explanation:
The value of a in the geometric series -2, 4, -8, ... is d) 8.
In a geometric series, each term is found by multiplying the previous term by a constant called the common ratio (r). In this series, the common ratio is -2. So, to get from -2 to 4, we multiply by -2, and to get from 4 to -8, we multiply by -2 again. Therefore, to find the next term, we multiply -8 by -2 to get 16, and so on.
Since the options are given as a), b), c), and d), we can see that the correct answer is d) 8 because the common ratio is -2, which means each term is obtained by multiplying the previous term by -2.