1/2+5/6+11/12+19/20+29/30+……+n平方-n-1/n(n-1)

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1/2+5/6+11/12+19/20+29/30+……+n平方-n-1/n(n-1)
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1/2+5/6+11/12+19/20+29/30+……+n平方-n-1/n(n-1)
1/2+5/6+11/12+19/20+29/30+……+n平方-n-1/n(n-1)

1/2+5/6+11/12+19/20+29/30+……+n平方-n-1/n(n-1)
一共n-1项
原式=(1-1/2)+(1-1/6)+(1-1/12)+(1-1/20)+(1-1/30)+.+( 1-1/n(n-1) )
= n-1 -(1/2+1/6+1/12+1/20+1/30+……+1/n(n-1))
= n-1 -(1-1/2 + 1/2-1/3 + 1/3-1/4 + 1/4-1/5 + 1/5-1/6 +.+ 1/(n-1)-1/n )
= n-1 -(1-1/n)
= n-2+1/n

原式=1-1/2+1-1/6+1-1/12+1.........
=n*1-(1/2+1/6+1/12+...+1/n(n-1))
=n-(1-1/2+1/2-1/3+1/3+1/4+.....-1/n)
=n-1+1/n