计算:-3/(1*2)+5/(2*3)-7/(3*4)+9/(4*5)-…+2005/(1002*1003)
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计算:-3/(1*2)+5/(2*3)-7/(3*4)+9/(4*5)-…+2005/(1002*1003)
因为 (2n+1)/n*(n+1)= =(n+n+1)/n*(n+1)=1/n+1/(n+1)
所以 -3/(1*2)+5/(2*3)-7/(3*4)+9/(4*5)-…+2005/(1002*1003
= -(1+2)/1*2+(2+3)/2*3-(3+4)/3*4+……+(1002+1003)/1002*1003
=-1-1/2+1/2+1/3-1/3-1/4+1/4+1/5-……+1/1002+1/1003
=-1+1/1003=1002/1003
所以 -3/(1*2)+5/(2*3)-7/(3*4)+9/(4*5)-…+2005/(1002*1003
= -(1+2)/1*2+(2+3)/2*3-(3+4)/3*4+……+(1002+1003)/1002*1003
=-1-1/2+1/2+1/3-1/3-1/4+1/4+1/5-……+1/1002+1/1003
=-1+1/1003=1002/1003
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