Question

Find the sum of a 9-term geometric sequence when the first term is 4 and the last term is 1,024 and select the correct answer below.

682
2,044
2,048
678

Answer 1

well you need to find the common ratio...

you know the 9th term is 1024

and the 1st term is 4

so use the formula for a term

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

so

\[1024 = 4\times r^8\]

solve for r.

the fund the sum of 9 terms using

\[S_{9} = \frac{4( 1 - r^9)}{1 - r}\]

hope it helps