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

 Apr 22, 2019
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Sum = a1 / (1-r) 

45 = a1 /(1- -1/2)

45 (1 1/2) = a1

= 1.5*45 = 67.5

 Apr 22, 2019

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