SOLUTION: Find the sum of the geometric sequence −3, 15, −75, 375, … when there are 7 terms and select the correct answer below. the options are: A) -39,063 B) 39,063 C) 58,593

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Question 1154282: Find the sum of the geometric sequence −3, 15, −75, 375, … when there are 7 terms and select the correct answer below.
the options are:
A) -39,063
B) 39,063
C) 58,593
D) -58,593
if you can, please include a thorough explanation!!! thanks!
Found 2 solutions by MathLover1, MathTherapy:
Answer by MathLover1(20849)   (Show Source): You can put this solution on YOUR website!

first we need nth term formula:
write given terms as follow:




:
in general

5th term

6th term

7th term


the sum of the first terms geometric sequence is:



Answer by MathTherapy(10552)   (Show Source): You can put this solution on YOUR website!
Find the sum of the geometric sequence −3, 15, −75, 375, … when there are 7 terms and select the correct answer below.
the options are:
A) -39,063
B) 39,063
C) 58,593
D) -58,593
if you can, please include a thorough explanation!!! thanks!
Use the formula for the sum of a GP: 

 ---- Substituting  

 

 

 

Sum of the 7 GP terms, or:  

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