Question

What is the sum of an 8-term geometric series if the first term is −11, the last term is 180,224, and the common ratio is −4?
A. -143,231
B. -36,047
C. 144,177
D. 716,144

Answer 1

The solution is attached as a word file

ff6504ada524d95e6ffc906d1de89d92.doc

Answer 2

$S_n = \dfrac{a_1(1 - r^n)}{1-r} \ , \ r\neq 1$

First term = -11, Last term = 180,224, Common Ratio = -4

Find the sum of 8 terms:

$S_8 = \dfrac{-11(1 - (-4)^8)}{1 - (-4)}$

$S_8 = \dfrac{-11(1 - 65536) }{5}$

$S_8 = \dfrac{-11(-65535) }{5}$

$S_8 = \dfrac{720885}{5}$

$S_8 = 144177$

Answer: (C) 144177