计算1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/(11×12×13),要过程

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计算1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/(11×12×13),要过程
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计算1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/(11×12×13),要过程
计算1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/(11×12×13),要过程

计算1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/(11×12×13),要过程
1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+…+1/(11×12×13)
=1/2×【1/(1×2)-1/(2×3)+1/(2×3)-1/(3×4)+1/(3×4)-1/(4×5)+…+1/(11×12)-1/(12×13)】
=1/2×【1/(1×2)-1/(12×13)】
=1/2×【1/2-1/156】
=1/2×77/156
=77/312

1/((n-1)*n*(n+1))=0.5*(1/(n-1)*n-1/n*(n+1))
根据这公式来推导,计算得
1/2×【1/(1×2)-1/(12×13)】
=1/2×(1/2-1/156)
=1/2×77/156
=77/312