赞 ww444 幼苗
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嗯,原式=2（1/8+1/24+1/48+1/80）+2（1/15+1/35+1/63）+1/3
=2[1/（2*4）+1/（4*6）+1/（6*8）+1/（8*10)]+2[1/(3*5)+1/(5*7)+1/(7*9)]+1/3
=[1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10]+[1/3-1/5+1/5-1/7+1/7-1/9]+1/3
=1/2-1/10+1/3-1/9+1/3
=(1/2-1/10)+(1/3-1/9+1/3)
=(5-1)/10+(3-1+3)/9=2/5+5/9=(18+25)/45=43/45
=2[1/（2*4）+1/（4*6）+1/（6*8）+1/（8*10)]+2[1/(3*5)+1/(5*7)+1/(7*9)]+1/3
=[1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10]+[1/3-1/5+1/5-1/7+1/7-1/9]+1/3
=1/2-1/10+1/3-1/9+1/3
=(1/2-1/10)+(1/3-1/9+1/3)
=(5-1)/10+(3-1+3)/9=2/5+5/9=(18+25)/45=43/45
1年前
4
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