设数列an是首项为a1(a1>0),公差为2的等差数列,其前n项和为Sn,且根号S1,根号S2.根号S3成等差数列.求a

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设数列an是首项为a1(a1>0),公差为2的等差数列,其前n项和为Sn,且根号S1,根号S2.根号S3成等差数列.求an的通项公式

a2=a1+d=a1+2 a3=a1+4 s1=a1 s2=a1+a2=2a1+2 s3=a1+a2+a3=3a1+6 根号S1+根号S3=2倍根号S2 根号a1+根号(3a1+6)=2倍根号(2a1+2) a1+3a1+6+2倍根号[a1(3a1+6)]=8a1+8 2a1+1=根号[a1(3a1+6)] 4a1平方+4a1+1=3a1平方+6a1 a1平方-2a1+1=0 a1=1 所以an=a1+（n-1)d=2n-1
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设数列{an}是首项为a1(a1>0),公差为2的等差数列,前n项和为Sn,且根号S1,根号S2,根号S3成等差数列, 设数列an是首项为a1(a1>0),公差为2的等差数列,其前n项和为Sn,且根号S1,根号S2.根号S3成等差数列.求a 设数列{An}是首项为a1,a1>0,公差为2地等差数列,其前N项和为Sn,且根号S1,根号S2,根号S3成等差数列.求设数列{an}是首项为a1(a1>0),公差为2的等差数列,其前n项和为Sn,且根号S1,S2,S3成等差数列.求数列{ #高考提分#设数列{an}是首项为a1(a1>0),公差为2的等差数列,前n项和为Sn,且根号S1,根号S2,根号S3成设数列(an)是首项为a1(a＞0),公差为2的等差数列,其前n项和为Sn,且√s1,√s2,√s3 数列an是首项为3公差为2的等差数列其前n项和为Sn求An=1/S1+1/S2+1/S3+...+1/Sn 已知等差数列{an的公差为2,前n项和为Sn,且S1,S2,S3成等比数列.(1)求数列{an的通项公式等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列.问：若a1-a3=3,求数列S1、S3、S2的公差d 已知等比数列{an}的前n项和为sn,a1=2,s1,2s2,3s3成等差数列,1.求数列{an}的通项公式已知等比数列｛an｝的前n项和为Sn,a1 ＝1.S1、2S2、3S3成等差数列,求数列｛an｝的通项公式已知数列an是首项为4公比为q的等比数列,sn是其前n项和,且4a1,a5,-2a3成等差数列,求设An=S1+S2+…