求和1/1×2+1/2×3+.+1/n(n+1)用裂项相消法如题,

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求和1/1×2+1/2×3+.+1/n(n+1)用裂项相消法如题,
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求和1/1×2+1/2×3+.+1/n(n+1)用裂项相消法如题,
求和1/1×2+1/2×3+.+1/n(n+1)用裂项相消法
如题,

求和1/1×2+1/2×3+.+1/n(n+1)用裂项相消法如题,
1/(1×2)+1/(2×3)+...+1/[n(n+1)]
=1-1/2+1/2-1/3+...+1/n -1(n+1)
=1- 1/(n+1)
=n/(n+1)

答:
1/1×2+1/2×3+....+1/n(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)