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  • 1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90怎么解(X/X=幾分之幾

    1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90怎么解(X/X=幾分之幾
    數(shù)學(xué)人氣:703 ℃時(shí)間:2019-10-25 16:49:52
    優(yōu)質(zhì)解答
    1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
    =1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)
    =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+1/8-1/9+1/9-1/10
    =1-1/10
    =9/10
    9/10-1/2=4/10=2/5
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