Đáp án:
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Bài `3`
`1,`
`A = (-3)/17 + (2/3 + 3/17)`
`↔A=(-3)/17 + 2/3 + 3/17`
`↔A=( (-3)/17 + 3/17) + 2/3`
`↔A=0 + 2/3`
`↔A=2/3`
Vậy `A=2/3`
`2,`
`B =(-5)/21 + ( (-16)/21 + 1)`
`↔B=(-5)/21 + (-16)/21 + 1`
`↔B= ( (-5)/21 + (-16)/21) + 1`
`↔B=-1+1`
`↔B=0`
Vậy `B=0`
`3,`
`C = ( (-1)/6 + 5/(-12) + 7/12`
`↔C = (-1)/6 + 5/(-12) + 7/12`
`↔C=(-1)/6 + (5/(-12) + 7/12)`
`↔C=(-1)/6 + 2/12`
`↔C=(-2)/12 + 2/12`
`↔C=0`
Vậy `C=0`
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Bài `4`
`a,`
`x = 3/4 + 1/(-12)`
`↔x=9/12 + 1/(-12)`
`↔x=2/3`
Vậy `x=2/3`
`b,`
`x/14 = 1/7 + (-3)/14`
`↔x/14 = 2/14 + (-3)/14`
`↔x/14 = (-1)/14`
`↔14x=-14`
`↔x=-14÷14`
`↔x=-1`
Vậy `x=-1`
`c,`
`8/17 + 5/17 < x/17 < 6/17 + 9/17 (x ∈ ZZ)`
`↔ 13/17 < x/17 < 15/17`
`↔13 < x < 15`
Do `x ∈ ZZ`
`↔x=14`
Vậy `x=14`
`d,`
`(-6)/7 + 3/35 < x/35 < (-2)/5 + 3/7 (x ∈ ZZ)`
`↔ (-30)/35 + 3/35 < x/35 < (-14)/35 + 15/35`
`↔ (-27)/35 < x/35 < 1/35`
`↔ -27 < x < 1`
Do `x ∈ ZZ`
`↔ x ∈ {-26;-25;...;-1;0}`
Vậy `x ∈ {-26;-25;...;-1;0}`
