谁能告诉我求1/2+1/6+1/12+1/20+……+1/420

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谁能告诉我求1/2+1/6+1/12+1/20+……+1/420谁能告诉我求1/2+1/6+1/12+1/20+……+1/420谁能告诉我求1/2+1/6+1/12+1/20+……+1/420原式=1

谁能告诉我求1/2+1/6+1/12+1/20+……+1/420
谁能告诉我求1/2+1/6+1/12+1/20+……+1/420

谁能告诉我求1/2+1/6+1/12+1/20+……+1/420
原式=1/（1*2）+1/（2*3）+1/（3*2）+1/（4*5）+……+1/（20*21）
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5-...-1/20+1/20-1/21
=1-(1/2-1/2)-(1/3-1/3)-(1/4-1/4)-...-(1/20-1/20)-1/21
=1-0-0-0-0-...-0-1/21
=1-1/21
=20/21

1/2=1-1/2
1/6=1/2-1/3
...
1/2+1/6+1/12+1/20+……+1/420=-1/21

找规律
1/2+1/6+1/12+1/20+……+1/420
=1/2+1/(2*3)+1/(3*4)+1/(4*5)+......+1/(20*21)
=1/2+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+......+(1/20-1/21)
=1/2+1/2-1/21
=1-1/21
=20/21

1/2+1/6+1/12+1/20+……+1/420
=1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+......+1/(20*21)
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+......+1/20-1/21
=1-1/21
=20/21

等于1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+......1/20-1/21
=1-1/21
=20/21

谁能告诉我求1/2+1/6+1/12+1/20+……+1/420 谁能告诉我6÷2（2+1）=9 求详细解答谁能告诉我1+1等于几谁能告诉我1+1等于几谁能告诉我1+1等于几? 谁能告诉我1+1=?数学谁能告诉我1等于几谁能告诉我1点成语谁能告诉我1/2 UNF和1/2 1+1为什么等于2啊?谁能告诉我,谢谢? 谁能告诉我1+1为什么等于2 谁能告诉我为什么1+1会等于2 谁能告诉我1到12月的英语单词是什么要是谁能告诉我1+5+6+8.2=? 谁能告诉我1+2等于几算不来谁能现在告诉我1,2,3,4象限位置谁能告诉我1倍和2倍的区别 1+1=?谁能告诉我一加一等于几?谁能告诉我1+1=几?