Question

What is the sum of an 8-term geometric series if the first term is 14 and the last term is -3,919,104?

Answer 1

well you need to find the common ratio.

to do this you need the information for the 8th term

a term in a geometric series is

\[a_{n} = a \times r^{n -1}\]

so you know

\[-3919104 = 14 \times r ^7\]

solve for r.

then the sum of a geometric series is

\[S_{8} = \frac{14( 1 - r^8)}{1 - r}\]

hope this helps.

Answer 2

−3919104=14×r^7
or r^7 = -279936
or r^7 = -(2*3)^7
hence r=-6 use as campbell_st has formulated

Answer 3

got to love the answer post... eliminates the need for learning.