SOLUTION: The sum of a geometric sequence 2 - 6 + 18 - 54 + ... - tn is - 29 524. Find the number of terms.

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Question 1202480: The sum of a geometric sequence 2 - 6 + 18 - 54 + ... - tn is - 29 524. Find the number of terms.
Answer by ikleyn(52788)   (Show Source): You can put this solution on YOUR website!
.
The sum of a geometric sequence 2 - 6 + 18 - 54 + ... - tn is - 29524.
Find the number of terms.
~~~~~~~~~~~~~~~ 

This geometric progression has the first term a= 2 and the common ratio -3.


Use the general formula for the sum of the first n terms

     = .


It gives

    -29524 = .


Simplify and find n

     = 

    59048 = 

    59048 + 1 = 

    59049 = 

     = 


It implies  n= 10.


ANSWER.  The number of terms is 10.

Solved.



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