Question

What is the sum of an 8-term geometric series if the first term is 12 and the last term is -3,359,232?

-3,599,175
-3,359,230
-3,119,285
-2,879,340

Answer 1

\[
12 a^7=-3359232 \\
a=- 6
\]

Answer 2

The terms are
{12, -72, 432, -2592, 15552, -93312, 559872, -3359232}

Answer 3

Their sum is -2879340

Answer 4

You can also apply the formula
\[
\frac{12
\left(1-a^8\right)}{1-a}=\frac{12
\left(1-(-6)^8\right)}{1+6}=-2879340
\]