已知等差数列{an}满足:a3=7,a1＋a11=26,{an}的前n项和为Sn,求an及Sn

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/10/02 17:31:30

a3=7,
a1+a11=2a6=26,a6=13
∴d=(a6-a3)/3=2
a1=a3-2d=3
∴an=3+2(n-1)=2n+1
Sn=(a1+an)n/2=(2n+4)n/2=n²+2n
这是我在静心思考后得出的结论,
如果不能请追问,我会尽全力帮您解决的~
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