SOLUTION: Please Help: Find the sum of the first five terms of the geometric sequence. a = 1, r = -3 A) 121 B) 61 C) -121 D) -61

Question 201893: Please Help:
Find the sum of the first five terms of the geometric sequence.
a = 1, r = -3
A) 121
B) 61
C) -121
D) -61

Answer by jim_thompson5910(35256) (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

Start with the given formula

Plug in , , and

Raise -3 to the 5th power to get -243

Subtract

Multiply

Divide

So the sum of the first five terms is 61 which means that the answer is B)
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