a (-7)/21+1+1/3

b 2/15+(5/9+6/9)

c((-1)/5+3/12)+(-3)/4

a 7/3+1/2=(-3)/70

b 5/12=3/16+3/4

`a, (-7)/21+1+1/3=(-1)/3+3/3+1/3=(-1+3+1)/3=3/3=1`

`b,2/15+(5/9+6/9)=2/15+11/9=(18+165)/135=183/135`

`c, ((-1)/5+3/12)+(-3)/4=(-1)/5+1/4+(-3)/4=(-1)/5+(1/4+(-3)/4)=(-1)/5-1/2=(-5-2)/10=(-7)/10`

`d, 7/3+1/2+(-3)/70=490/210+105/210-9/210=586/210=293/105`

`e, 5/12+3/16+3/4=20/48+9/48+36/48=65/48`

Đáp án:

a) (-7)/21+1+1/3

<=> -1/3+1+1/3

<=> 1+ ( -1/3+1/3)

<=> 1+0

<=> 1

b) 2/15+(5/9+6/9)

<=> 2/15+11/9

<=> 6/45+55/45

<=> 61/45

c) ((-1)/5+3/12)+(-3)/4

<=> ( -12/60 + 15/60 ) - 3/4

<=> 3/60 - 3/4

<=> 1/20 - 15/20

<=> -14/20 = -7/20

d) 7/3+1/2=(-3)/70

<=> 7/3+1/2 - (-3)/70

<=> ( 7/3+1/2 ) - (-3)/70

<=> (  14/6 + 3/6 ) - (-3)/70

<=> 17/6 - (-3)/70

<=> 302/105

e) 5/12=3/16+3/4

<=> 3/16+3/4 - 5/12

<=> ( 3/16+3/4 ) - 5/12

<=> ( 3/16+ 12/16 ) - 5/12

<=> 15/16 - 5/12

<=> 45/48 - 20/48

<=> 25/48

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