Question 593132
if 3,9,27 is a geometric sequence with common ratio of 3.
a(n) = a(1)*r^(n-1)
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(a)find the value of 10 term
a(10) = 3*3^9 = 3^10
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(b)sum of first 15 term
S(n) = a[(1-r^n)/(1-r)]
S(15) = 3[(1-3^15)/(-2)] = 21,523,359
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(2)suppose we have 8,16,32,64. 
(a)find the value of the 20term 
(b)sum of the first 15term
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Use the formulas.
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Cheers,
Stan H.
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