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What is the sum of the first 8 terms of the geometric series?

120-80+160/3-320/9+...

Express your answer as a simplified fraction.

 Jan 25, 2020
 #1
avatar+18319 
+1

The common ratio for this series is -2/3     --->     r  =  -2/3

The first term is 120                                   --->     a  =  120

There are 8 terms                                      --->     n  =  8

The formula is                                            --->    Sum  =  a · [ (1 - rn) / (1 - r) ]

 

Sum  =  120 · [ ( 1 - (-2/3)8 ) / ( 1 - (-2/3) ) ]

 

Now, it's calculator time!

 Jan 25, 2020

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