Question

What is the sum of an 8-term geometric series if the first term is 13 and the last term is -3,639,168?

Answer 1

common ratio of terms
\[= \sqrt[7]{-3,639,168/13} = -6\]
Sum of GS
\[=\frac{a(r^n-1)}{r-1} =\frac{13((-6)^8-1)}{(-6)-1} = ? \]