What is the sum of the geometric sequence -4,24,-144,... if there are 8 terms?

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Answer 1 · 2018-05-17T05:11:33

#959780#

Sum of geometric sequence is #(a(r^n-1))/(r-1)#
where
a = your first number
r = the ratio
n = number of terms

In this case,

a = -4
r = #24/-4 = -144/24 = -6#
n = 8

Sum
= #(a(r^n-1))/(r-1)#

= #(-4((-6)^8-1))/(-6-1)#

= #(-4times1679615)/-7#

= #-6718460/-7#

= #959780#