设数列{an}的前n项和Sn=n^2-4n+1,则/a1/+/a2/+/a3/+……+/a10/=
需详细过程。
人气:354 ℃ 时间:2019-08-28 01:17:42
解答
a1=s1=1^2-4*1+1=-2
sn=n^2-4n+1
s(n-1)=(n-1)^2-4(n-1)+1
=n^2-2n+1-4n+4+1
=n^2-6n+6
an=sn-s(n-1)
=n^2-4n+1-(n^2-6n+6)
=n^2-4n+1-n^2+6n-6
=2n-5
an>0
2n>5
n>2.5
即当n=3时an>0
a2=2*2-5=-1
a3=2*3-1=1
a10=2*10-5=15
/a1/+/a2/+/a3/+……+/a10/
= /a1/+/a2/+a3+……+a10
= /-2/+/-1/+(1+15)*8/2
=2+1+64
=67
推荐
- 已知数列{an}中,a1=1,前n项和sn=(n+2)an/3,求a2,a3求{an}的通项公式
- 已知数列{an}中,a1=1,前n项和Sn=n+2/3an (1)求a2,a3; (2)求{an}的通项公式.
- 若数列an满足a1=1,an+a(n+1)=(1/4)^n ,设Sn=a1+4*a2+4^2*a3+……+4^(n-1)*an,
- 数列{an}前n项和Sn=n2-4n+1,则|a1|+|a2|+|a3|+…+|an|=
- 设数列{an}的前n项和为Sn满足2Sn=an+1-2n+1+1,n∈N*,且a1,a2+5,a3成等差数列.(1)求a1的值;(2)求数列{an}的通项公式.
- 改错:Noddles are popular in China.
- 抛物线y=a(x+h)²与直线y=ax+b相交于点(-1,1),且抛物线的对称轴为x=-2.求抛物线y=a(x+h)²和直线y=ax+b的解析式
- He always talks的同义句
猜你喜欢