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Hello, I've tried these problems out already, I'm just a little stuck. I appreciate all your help. Thanks.

(Also, if you can explain how you came up with the answer, that would also be great so that I can learn), Thanks much.

 

1.

What is the sum of the first eight terms of the series?

 

(−500)+(−100)+(−20)+(−4)+(−0.8)+...

 

Round the answer to two decimal places if necessary.

−996.09

 

−625

 

−624.99

 

−623

 

2.

What is the sum of the first 7 terms of the series  −3+6−12+24−... ?

Guest Apr 9, 2018
 #1
avatar+89729 
+1

1. First eight terms  ..... (−500)+(−100)+(−20)+(−4)+(−0.8)+...

 

The common ratio is  (1/5)....the sum, S, is given by :

 

S  =  First Term  [  1 -  common ratio^8] / [ 1 - common ratio ]  =

 

S  =  -500  [  1  - (1/5)^8] / [ 1 - 1/5]   =  -[ 624  + 624/625 ]  ≈  -624.99

 

 

2.  What is the sum of the first 7 terms of the series  −3+6−12+24−... ?

 

The common ratio  is  -2

 

The sum, S, is given by :

 

S  =  -3  [ 1  - (-2)^7 ] / [  1 - (-2) ]   = -129

 

 

cool cool cool

CPhill  Apr 9, 2018

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