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An infinite geometric series has common ratio -1/3 and sum 25.  What is the second term of the sequence?

supermanaccz  Mar 21, 2018
 #1
avatar+628 
+1

I got it, but you can answer anyways. 

supermanaccz  Mar 21, 2018
 #2
avatar+92477 
+1

We can find the first term a1, thusly

 

a1

____    =  Sum             .......so......

1 - (r)

 

  a1

_______    =    25

1 - (-1/3)

 

 

  a1

____   =  25           multiply both sides by 4/3

  4/3

 

 

a1  =  25 (4/3)  =  100/3

 

So.....the second term is   (100/3) (-1/3)  =  -100 / 9

 

 

cool cool cool

CPhill  Mar 21, 2018
 #3
avatar+628 
+1

Thank you so much!

supermanaccz  Mar 21, 2018

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