Sn=1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/n×(n+1)×(n+2)=___.
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Sn=1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/n×(n+1)×(n+2)=___.
![Sn=1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/n×(n+1)×(n+2)=___.](/uploads/image/z/17054120-56-0.jpg?t=Sn%3D1%2F%281%C3%972%C3%973%29%2B1%2F%282%C3%973%C3%974%29%2B1%2F%EF%BC%883%C3%974%C3%975%EF%BC%89%2B%E2%80%A6%2B1%2Fn%C3%97%EF%BC%88n%2B1%EF%BC%89%C3%97%EF%BC%88n%2B2%EF%BC%89%3D___.)
把1/(1×2×3)化成1/2 - 1/3,1/(2×3×4)化成1/6 - 1/12,以此类推.,试一试,你会发现中间这些会被削掉的
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