1.如果1+x,10+x和46+x形成一個等比序列,求x的值.
2.一個等比序列中,T(1)．T(4)=64和T(3)=16.求該等比序列我通項T(n).
步驟thx
等差&等比數列
2008-08-10 6:40 am
回答 (1)
2008-08-11 5:17 am
✔ 最佳答案
1/ (10+x) / (1+x) = (46+x) / (10+x)x^2+20x+100 = x^2+47x+46
27x = 54
x = 2
2 / T(1) = x, T(4) = x*r^(4-1)
T(3) = x*r^2 = 16---------(A)
T(1)*T(4) = 64 -----> x*x*r^3=64
x^2*r^3=64--------(B)
(A)/(B) : x*r=4
when x*r=4, r=4,x=1 (將x*r 代入(A)內)
so...T(n) = 4^(n-1)
參考: my knowledge~*
收錄日期: 2021-04-29 21:54:12
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080809000051KK02808