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If a geometric series is given by an= 2 * (1/3)^x, find a2, find S, and find S3

 Sep 3, 2016
 #1
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54 = 76

 Sep 3, 2016
 #2
avatar+9673 
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I suppose you mean an= 2 * (1/3)^n

a2 

\(=2\times(\dfrac{1}{3})^2\\ =\dfrac{2}{9}\) 

 

 

SOR S 

\(=\dfrac{a_1(1-r^n)}{1-r}\\ =\dfrac{2\times(\dfrac{1}{3})^1\times(1-\dfrac{1}{3^n})}{1-\dfrac{1}{3}}\\ =\dfrac{3^n-1}{3^n}\)

 

 

S3

\(=\dfrac{3^3-1}{3^3}\\ =\dfrac{26}{27}\)

 Sep 4, 2016

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