设等差数列的前n项和为Sn,前2n项和为S2n,前3n项和为S3n,求证S3n=3(S2n-Sn)
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设等差数列的前n项和为Sn,前2n项和为S2n,前3n项和为S3n,求证S3n=3(S2n-Sn)设等差数列的前n项和为Sn,前2n项和为S2n,前3n项和为S3n,求证S3n=3(S2n-Sn)设等
设等差数列的前n项和为Sn,前2n项和为S2n,前3n项和为S3n,求证S3n=3(S2n-Sn)
设等差数列的前n项和为Sn,前2n项和为S2n,前3n项和为S3n,求证S3n=3(S2n-Sn)
设等差数列的前n项和为Sn,前2n项和为S2n,前3n项和为S3n,求证S3n=3(S2n-Sn)
直接利用等差数列求和公式,带入化简即可.
或者直接分析也行,(S3n-S2n)-(S2n-Sn)=S2n-Sn-Sn,移个项就搞定了.
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