SOLUTION: Please Help: Find the sum of the first five terms of the geometric sequence. a = 1, r = 2 A) 31/5 B) 91/3 C) 31 D) 91/15

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Question 201897: Please Help:
Find the sum of the first five terms of the geometric sequence.
a = 1, r = 2
A) 31/5
B) 91/3
C) 31
D) 91/15
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
The formula for the sum of the first "n" terms of any geometric sequence is S=%28a%28r%5En-1%29%29%2F%28r-1%29


S=%28a%28r%5En-1%29%29%2F%28r-1%29 Start with the given formula


S=%281%282%5E5-1%29%29%2F%282-1%29 Plug in a=1, r=2, and n=5


S=%281%2832-1%29%29%2F%282-1%29 Raise 2 to the 5th power to get 32


S=%281%2831%29%29%2F%281%29 Subtract


S=%2831%29%2F%281%29 Multiply


S=31 Divide


So the sum of the first five terms is 31 which means that the answer is C)