Đáp án:

Bài `1`

Từ đẳng thức : `3 × 4 = 6 × 2`

`->` \(\left\{ \begin{array}{l}\dfrac{3}{2}=\dfrac{6}{4}\\ \dfrac{3}{6}=\dfrac{2}{4}\\ \dfrac{6}{3}=\dfrac{4}{2}\\ \dfrac{2}{3}=\dfrac{4}{6}\end{array} \right.\)

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Bài `2`

`a,`

`(10 + 5)/(4 × 5)`

`= 15/(4 × 5)`

`= (3 × 5)/(4 × 5)`

`= 3/4`

`b,`

`(2^2 × 9)/(27 × 2)`

`= (2^2 × 3^2)/(3^3 × 2)`

`= (2 × 1)/(3 × 1)`

`= 2/3`

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Bài `3`

Vì `hat{zOt}` và `hat{xOy}` là 2 góc bù nhau

`-> hat{xOy} + hat{zOt} = 180^o`

`-> hat{xOy} = 180^o - hat{zOt}`

`-> hat{xOy} = 180^o - 50^o`

`-> hat{xOy} = 130^o`

Vậy `hat{xOy}  = 130^o`

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Bài `4`

`1,`

`2 1/3 × 3`

`= 7/3 × 3`

`= 7`

`2,`

`(2/5 - 3/4) - 2/5`

`= 2/5 - 3/4 - 2/5`

`= (2/5 - 2/5) - 3/4`

`= -3/4`

`3,`

`(-10)/11 × 4/7 + (-10)/11 × 3/7 + 1 10/11`

`= (-10)/11 × (4/7 + 3/7) + 21/11`

`= (-10)/11 × 1 + 21/11`

`= (-10)/11 + 21/11`

`= 1`

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Bài `5`

`1,`

`3/5 - x = 0,2`

`-> x = 3/5 - 0,2`

`-> x=2/5`

Vậy `x=2/5`

`2,`

`x/3 - 1/8 = 5/8`

`-> x/3 = 5/8 + 1/8`

`-> x/3=3/4`

`->4x =3 × 3`

`-> 4x=9`

`-> x=9/4`

Vậy `x=9/4`

`3,`

`3 1/3x - 6 3/4 = 3 1/4`

`-> 10/3x - 27/4 = 13/4`

`-> 10/3x = 13/4 + 27/4`

`-> 10/3x=10`

`-> x=10÷10/3`

`-> x=3`

Vậy `x=3`

Bài `1:`

`3/6 = 2/4`

`6/3 = 4/2`

`3/2 = 6/4`

`2/3 = 4/6`

Bài `2:`

`a)  (10 + 5)/(4 . 5) = (15)/(4.5) = (3.5)/(4.5) = 3/4`

`b)  (2^2 . 9)/(27.2) = (2.2.9)/(27.2) = (2.9)/27 = (2.9)/(9.3) = 2/3`

Bài `3:`

Vì `\hat{xOy}` và `\hat{zOt}` là hai góc bù nhau

`=> \hat{xOy} + \hat{zOt} = 180^o`

`=> \hat{xOy} + 50^o = 180^o`

`=> \hat{xOy} = 130^o`

Bài `4:`

`2 1/3 . 3 = 7/3 . 3 = 21/3 = 7`

`(2/5 - 3/4) - 2/5`

`= 2/5 - 3/4 - 2/5`

`= (2/5 - 2/5) - 3/4`

`= 0 - 3/4`

`= (-3)/4`

`(-10)/11 . 4/7 + (-10)/11 . 3/7 + 1 10/11`

`= (-10)/11 . (4/7 + 3/7) + 21/11`

`= (-10)/11 . 1 + 21/11`

`= (-10)/11 + 21/11`

`= 1`

Bài `5:`

`3/5 - x = 0,2`

`=> 0,6 - x = 0,2`

`=> x = 0,6 - 0,2`

`=> x = 0,4`

`x/3 - 1/8 = 5/8`

`=> x/3 = 5/8 + 1/8`

`=> x/3 = 3/4`

`=> x . 4 = 3 . 3`

`=> x.4 = 9`

`=> x = 9/4`

`3 1/3 . x - 6 3/4 = 3 1/4`

`=> 10/3 . x - 27/4 = 13/4`

`=> 10/3 . x = 13/4 + 27/4`

`=> 10/3 . x = 10`

`=> x = 10 : 10/3`

`=> x = 3`