1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+1/55+1/66+1/78+1/91+1/105+1/120+1 =1/3(1+1/2)+1/5(1/2+1/3)+1/7(1/3+1/4)+1/9(1/4+1/5)+1/11(1/5+1/6)+1/13(1/6+1/7)+1/15(1/7+1/8)+1 =1/2+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1 =(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 =1-1/8+1 =15/8 =1又8分之7
1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+…+1/105+1/120+1 =2*(1/6+1/12+1/20+1/30+1/42+1/56+1/72+…+1/210+1/240)+1 =2*[(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+…+(1/15-1/16)]+1 =2*(1/2-1/16)+1 =15/8.
解：两个一组加一加……可以先通分，发现可以约分的，暂时不用算出来…… 原式=1-1/2+1/2-1/3+……+1/7-1/8+1 =2-1/8 =15/8
答：最好一题一问 下面仅提供思路和答案. 1、P=1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45 通项为 2/[(n+1)(n+2)=2...详情>>
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