等比数列an前n项和为sn=2^n+1+b 求b
人气：472 ℃ 时间：2020-05-12 00:28:13
解答
a1=S1=2^1+1+b=3+b
a2=S2-S1=2^2+1+b-(3+b)=2
a3=S3-S2=4
等比则a2²=a1a3
所以b=-2
推荐
- 等比数列{an}的前n项和sn=a*2^n+a-2,则an=?
- 在等比数列{an}中,a1=2,前n项和为Sn,若数列{an+1}也是等比数列,则Sn等于?
- 在等比数列{an}中，a1=2，前n项和为Sn，若数列{an+1}也是等比数列，则Sn等于（ ） A.2n+1-2 B.3n C.2n D.3n-1
- 已知等比数列an的前n项和Sn=2^n-1,则a1^2+a2^2+...an^2=?
- 已知数列{an}的前n项和为Sn,且Sn=（1/2）^n+a,若{an}为等比数列,则a=?
- 若ABC0,则A、B、C中负数()
- Many of creatures in the movie Avater are not real,but much of _____happens is still attractive ...
- Sorry unintentionally hurt you hope you have a brand new start tomorrow
猜你喜欢
