Question

What is the sum of a 7-term geometric series if the first term is −11, the last term is −171,875, and the common ratio is −5?

−143,231
−36,047
144,177
716,144

Answer 1

the formula for the sum of a geometric series is
\[ \sum_{i=0}^n a\ r^i=a \frac{1-r^{n+1}}{1-r} \]
where a is the first term, r is the common ratio, and in your case, n is 6