請問 1. (x-2)x小於-1 ，大於等於1 ，求X的範圍? 2. 若一數列a_n，a_1等於1，則(a_(n+1))等於(a_n)/2+1，求a_n等於多少?高中 回應 David Re: 請教教我吧 2006-10-04 21:48 2. 2-(1/2)^(n-1) Christine~P Re: 請教教我吧 2006-10-05 15:10 不好意思~~ 我需要完整的解題程式~~ = = David Re: 請教教我吧 2006-10-05 23:44 a_n =(a_(n-1))/2+1 =((a_(n-2)/2+1)/2+1 =... =a_1/2^n+a_1/2^(n-1)+a_1/2^(n-2)+...+1 =(1-1/2^n)/(1-1/2) =2-(1/2)^(n-1) David Re: 請教教我吧 2006-10-05 23:46 我覺得第一題有打錯耶 除非是"或"
David Re: 請教教我吧 2006-10-05 23:44 a_n =(a_(n-1))/2+1 =((a_(n-2)/2+1)/2+1 =... =a_1/2^n+a_1/2^(n-1)+a_1/2^(n-2)+...+1 =(1-1/2^n)/(1-1/2) =2-(1/2)^(n-1)
回應
David
Re: 請教教我吧
2006-10-04 21:482-(1/2)^(n-1)
Christine~P
Re: 請教教我吧
2006-10-05 15:10我需要完整的解題程式~~
= =
David
Re: 請教教我吧
2006-10-05 23:44=(a_(n-1))/2+1
=((a_(n-2)/2+1)/2+1
=...
=a_1/2^n+a_1/2^(n-1)+a_1/2^(n-2)+...+1
=(1-1/2^n)/(1-1/2)
=2-(1/2)^(n-1)
David
Re: 請教教我吧
2006-10-05 23:46除非是"或"