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An infinite geometric series has common ratio -1/2 and sum 45. What is the first term of the series?

 Dec 20, 2018
 #1
avatar+100586 
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Using the sum of an infinite series, we have :

 

a1  /  [ 1 - r ]  = the sum

 

Where a1 is the first term  and  r is the common difference.....so we have...

 

a1  / [ 1 - (-1/2) ] =  45     simplify

 

a1 /  [ 3/2]  =  45

 

a1 =  45 (3/2)

 

a1  =  67.5

 

 

cool cool cool

 Dec 20, 2018
 #2
avatar+866 
0

Thank you, CPhill! Perfect! 

ant101  Dec 22, 2018

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