奥数计算题,简便计算1 1 1 1 1 1 ---- + --- + --- +… --- + --- --- 6 12 20 72 90 110

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奥数计算题,简便计算1     1     1       1     1   1 ---- + --- + --- +… --- + --- ---  6     12    20       72    90  110

奥数计算题,简便计算1 1 1 1 1 1 ---- + --- + --- +… --- + --- --- 6 12 20 72 90 110
奥数计算题,简便计算
1 1 1 1 1 1
---- + --- + --- +… --- + --- ---
6 12 20 72 90 110

奥数计算题,简便计算1 1 1 1 1 1 ---- + --- + --- +… --- + --- --- 6 12 20 72 90 110
1/6=1/(2×3)=1/2-1/3
1/12=1/(3×4)=1/3-1/4
1/20=1/(4×5)=1/4-1/5
……
1/72=1/(8×9)=1/8-1/9
1/90=1/(9×10)=1/9-1/10
1/110=1/(10×11)=1/10-1/11
∴原式=1/(2×3)+1/(3×4)+1/(4×5)+……+1/(8×9)+1/(9×10)+1/(10×11)
=1/2-1/3+1/3-1/4+1/4-1/5+……+1/8-1/9+1/9-1/10+1/10-1/11
=1/2-1/11=9/22

2=1*2
6=2*3
20=4*5
=1-1/2+1/2-1/3+1/3-1/4......+1/10-1/11
中间全部减去
=1-1/11
=10/11
不懂在HI上问我

原式=1/2-1/11=9/22