5,15,45,135..的general term(通項)

2010-09-12 4:53 am

如題~求5,15,45,135, ...的general term(通項)

回答 (3)

2010-09-18 5:19 am

✔ 最佳答案

設T(n)=第n個數：
T(1)=5
T(2)=15
T(3)=45
T(4)=135
T(2)/T(1)=3
T(3)/T(2)=3
T(4)/T(3)=3
T(n)=5[3^(n-1)]
(P.S. x^0=1)

參考: Hope I can help you ^_^

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2010-09-12 6:43 am

general term=5(3^n - 1)
Sum of Geometric seqenuce=5(3^n - 1)/2

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2010-09-12 4:56 am

5,15,45,135,...
T(1) = 5 = a
T(2) = 15
T(3) = 45
T(4) = 135
R = T(2)/T(1) = T(3)/T(2) = 3
General term
= a(R^n - 1)/(R - 1)
= 5(3^n - 1) / 2

參考: Hope the solution can help you^^”

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