1/2+1/4-1/4+1/6-1/6+1/8-1/8+...+1/2010-1/2012

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• 1/2+1/4-1/4+1/6-1/6+1/8-1/8+...+1/2010-1/2012
• 1*2*3*4分之1+2*3*4*5分之1+…+17*18*19*20分之1（计算题）1/1*2*3*4+1/2*3*4*5…………+1/17*18*19*20=1/2(1/1*4-1/2*3+1/2*5-1/3*4+1/3*6-1/4*5……1/17*20-1/18*19)=1/2(1/1*4+1/2*5+1/3*6……1/17*20-(1/2*3+1/3*4……1/18*19))=1/2*(1/3*(1-1/4+1/2-1/5+1/3-1/6+1/4-1/7……1/17-1/20)-(1/2-1/3+1/3-1/4……1/18-1/19))=1/2*(1/3*(1+1/2+1/3-1/18-1/19-1/20)-(1/2-1/19))=1/2*(1/3*(5/18-1/19-1/20+3/19))=1/6*(5/18+2/19-1/20)=1139/(6*19*180)=1139/20520
• 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=______1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90 ＝1/（1*2）+1/（2*3）+1/（3*4）+1/（4*5）+1/（5*6）+1/（6*7）+1/（7*8）+1/（8*9）+1/（9*10） ＝1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10 ＝1-1/10 ＝9/10本人已知道答案,不过还是不太懂,是啊...的确很难,直接用文字解释可以吗?本人只是刚上初中而已...
• (—2)+4+(—6)+8+...+(—2010)+2012
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