1. 6/(1-1/5)/(1-1/4)/(1-1/4)/(1-1/2)=80/3
2. 2004*[1/5+1/(5*9)+1/(13*9)+1/(13*17)+1/(17*21)]=(2004/4)*(1-1/5+1/5-1/9+1/9-1/13+1/13-1/17+1/17-1/21)=3340/7
1,6*(5/4)*(4/3)*(3/2)*(2/1)=30
2,原式=2004*[1/5+1/(5*9)+1/(13*9)+1/(13*17)+1/(17*21)]=(2004/4)*(1-1/5+1/5-1/9+1/9-1/13+1/13-1/17+1/17-1/21)=501*(1-1/21)=10020/21
1. 6/(1-1/5)/(1-1/4)/(1-1/4)/(1-1/2)=80/3
2. 通分即可
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