快遞百科

標題:

A.S. and G.S.

發問:

The sum to infinity of a geometric sequence is 81 and the sum of all its odd terms[ i.e. T(1) + T(3) + T(5) + T(7) +...... ] is 121.5 . (a)Find the common ratio (b)Find T(1) 更新: a/(1-R^2)=121.5 ......點出呢個架??

最佳解答:

let T(n)=aR^(n-1) , then T(n+2)=aR^(n+1) so the common ratio is R^2 , i.e. a/(1-R^2)=121.5--(1) and a/(1-R)=81--(2) (2)/(1)=(1-R)(1+R)/(1-R)=2/3 =>1+R=2/3 , R=-1/3 // a/(1-R)=81 =>a/(1+1/3)=81 =>a/(4/3)=81 =>a=108//

• Z ZETA GUNDAM MASTER GRADE 說明書
• C朗拿度PHOTO
• 急要.junie B. jones and mushy gushy valentime的內容

此文章來自奇摩知識+如有不便請留言告知

其他解答: