1/2+1/6+12/+20/+30/+……+1/110=?

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1/2+1/6+12/+20/+30/+……+1/110=?
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1/2+1/6+12/+20/+30/+……+1/110=?
1/2+1/6+12/+20/+30/+……+1/110=?

1/2+1/6+12/+20/+30/+……+1/110=?
原式为可化为
1/1×2 + 1/2×3 + 1/3×4 + 1/4×5 +1/5×6 + ...+ 1/10×11
注意到:1/1×2=1-1/2
1/2×3=1/2-1/3
1/3×4=1/3-1/4
………………
1/10×11=1/10-1/11
故原式=(1-1/2)+(1/2-1/3)+(1/3-1/4)+...+(1/10-1/11)
=1-1/2+1/2-1/3+1/3-1/4+...+1/10-1/11
=1-1/11
=10/11

1-1/11=10/11