.a(a+1）分之1+(a+1)(a+2)分之1+（a+2)(a+3)+``````+(a+2004)(a+2005）分
.a(a+1）分之1+(a+1)(a+2)分之1+（a+2)(a+3)+``````+(a+2004)(a+2005）分之1
赞 sixsun0818 幼苗
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1/(a+n)(a+n+1)=1/(a+n)-1/(a+n+1)
a(a+1）分之1+(a+1)(a+2)分之1+（a+2)(a+3)+``````+(a+2004)(a+2005）分之1
=1/a-1/(a+1)+1/(a+1)-1/(a+2)+.+1/(a+2004)-1/(a+2005)
=1/a-1/(a+2005)
=2004/(a^2+2005a)
a(a+1）分之1+(a+1)(a+2)分之1+（a+2)(a+3)+``````+(a+2004)(a+2005）分之1
=1/a-1/(a+1)+1/(a+1)-1/(a+2)+.+1/(a+2004)-1/(a+2005)
=1/a-1/(a+2005)
=2004/(a^2+2005a)
1年前
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