数列1/3.1/15.1/35.1/63······的前n项和sn
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数列1/3.1/15.1/35.1/63······的前n项和sn数列1/3.1/15.1/35.1/63······的前n项和sn数列1/3.1/15.1/35.1/63······的前n项和sn1
数列1/3.1/15.1/35.1/63······的前n项和sn
数列1/3.1/15.1/35.1/63······的前n项和sn
数列1/3.1/15.1/35.1/63······的前n项和sn
1/3+1/15+1/35+1/63+.+1/(2n-1)(2n+1)
=1/2*[1-1/3+1/3-1/5+1/5-1/7+.+1/(2n-1)-1/(2n+1)]
=1/2*[1-1/(2n+1)]
=n/(2n+1)