the sum to the nth term of a geometric sequence is given by S(n)=4(3^n-1).
(a) Find the general term of the sequence.
(b)Find T(3)+T(5)+T(7).
MATHS F6
2012-09-17 2:10 am
回答 (1)
2012-09-17 2:40 am
✔ 最佳答案
(a) S(n) = a(r^n - 1)/(r - 1)So, we have r = 3 and a/(r - 1) = 4 => a = 8
general term : 8 * 3^(n - 1)
(b) T(3) = 8 * 3^2 = 72
T(5) = 8 * 3^4 = 648
T(7) = 8 * 3^6 = 5832
T(3) + T(5) + T(7) = 72 + 648 + 5832 = .6552
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