设数列{An}满足a1＝1.Sn＝a1＋a2＋a3＋…＋an＝n2 （1）当n>=2时.求Sn-Sn-1

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设数列{An}满足a1＝1.Sn＝a1＋a2＋a3＋…＋an＝n2 （1）当n>=2时.求Sn-Sn-1
（2）求数列的通项公式An

1.
Sn=A1+A2+A3+……+An=n^2
S(n-1)=A1+A2+A3+……+A(n-1)=(n-1)^2
Sn-S(n-1)=n^2-(n-1)^2=2n-1
2.
n>=2时
An=Sn-S(n-1)=2n-1
经验算A1=1也满足上式

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