-1/6-1/12-1/20-1/30……-1/420
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-1/6-1/12-1/20-1/30……-1/420
1/6-1/12-1/20-1/30……-1/420
不要只写答案
1/6-1/12-1/20-1/30……-1/420
不要只写答案
-1/(2*3)-1/(3*4)-1/(4*5)-1/(5*6)-.-1/(19*20)-1/(20*21)
=-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-...-(1/19-1/20)-(1/20-1/21)
=-1/2+1/3-1/3+1/4-1/4+1/5-...-1/19+1/20-1/20+1/21
=-1+1/21
=-20/21
=-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-...-(1/19-1/20)-(1/20-1/21)
=-1/2+1/3-1/3+1/4-1/4+1/5-...-1/19+1/20-1/20+1/21
=-1+1/21
=-20/21
谁能告诉我求1/2+1/6+1/12+1/20+……+1/420
1/2+1/6+1/12+1/20+1/30+……+1/9900 是多少?
1/2+1/6+1/12+1/20+1/30+……+1/90=?
1/2 + 1/6 + 1/12 + 1/20 + 1/30 …… + 1/90.
1/6+1/12+1/20+1/30+1/42+……+1/132等于多少
计算:1/6+1/12+1/20+1/30……+1/2009*2010 简便计算
简便计算 1/6+1/12+1/20+1/30+……1/2008*2009
1/6+1/12+1/20+1/30+……+1/9900=?
计算1/2-1/6-1/12-1/20-1/30-1/42…-1/132.
谁知道 2/1+6/1+12/1+20/1+30/1+…+9900/1 等于多少?
(1/2)+(1/6)+(1/12)+(1/20)+(1/30)+.+(1/420)
计算:1又1/2+2又1/6+3又1/12+4又1/20……+20又1/420=