1×1/2+1/2×1/3+1/3×1/4+.1/n×1/(n+1)怎么做RT

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1×1/2+1/2×1/3+1/3×1/4+.1/n×1/(n+1)怎么做
RT

1×1/2+1/2×1/3+1/3×1/4+.1/n×1/(n+1)
=1-1/2+1/2-1/3+1/3-1/4+.1/n-1/(n+1)
=1-1/(n+1)
=n/(n+1)