21. a, 3 7 10 5 _ ____ + ____ – _____+ _____ 13 12 13 12 b, 15/24 – 6/26 + 28/48 – 30/39 +10/24 c,-1/

Bởi

21.
a, 3 7 10 5
_ ____ + ____ – _____+ _____
13 12 13 12
b, 15/24 – 6/26 + 28/48 – 30/39 +10/24
c,-1/2 + 3/7 – 1/9 – 7/18 + 4/7
d,-5/10 + 12/28 – 3/27 +20/35
22.
a, lxl – 7/6 =4/15

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  1. a)-3/13+7/12-10/3+5/12=(-3/13-10/13)+(7/12+5/12)=-13/13+12/12=-1+1=0

     b)15/24-6/26+28/48-30/39+10/24=5/8-3/13+7/12-10/13+5/12=5/8+(-3/13)+7/12+(-10/13)+5/12=5/8+[(-3/13)+(-10/13)]+(7/12+5/12)=5/8+(-1)+1=5/8

    c)-1/2+3/7-1/9-7/18+4/7=-1/2+3/7+(-2/18)+(-7/18)+4/7=-1/2+(3/7+4/7)+[(-2/18)+(-7/18)]=-1/2+1+(-1/2)=1+[-1/2+(-1/2)]=1+(-1)=0

    d)-5/10+12/28-3/27+20/35=-1/2+3/7-1/9+4/7=-1/2+(3/7+4/7)-1/9=-1/2+1-1/9=1+[-1/2-1/9]=1+[-1/2+(-1/9)]=1+[-9/18+(-2/18)]=1+(-11/18)=18/18+(-11/18)=7/18

    22

    a)|x|-7/6=4/15

    =>|X|=4/15+7/6

    =>|x|=8/30+35/30

    =>|x|=43/30

    =>x=43/30 hoặc x=-43/30

    Vậy x=43/30 hoặc x=-43/30

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