Question

What is the sum of the geometric sequence –4, 24, –144, … if there are 6 terms?
a. –159,963
b. 26,660
c. 26,661
d. 159,963

I think its b, am i right?

Answer 1

well you need the common ratio found by

\[\frac{T _{2}}{T _{1}}=\frac{T _{3}}{T _{2}}...\]

as this is an alternating sequence the common ratio is negative

then use the formula

\[s _{6}=\frac{-4(r^6 -1)}{r-1}\]

Answer 2

yea thanks i did that but im jsut checking to see if someone else got that answer as well.

Answer 3

use wolfram if you just want to check

Answer 4

ok thanks~!