`a) 3/7 - 1/21x = 1/3`
`1/21 x = 3/7 - 1/3`
`1/21 x = 2/21`
`x = 2/21 : 1/21`
`x = 2`
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`b) 7/6 - x : 3/4 = |-1/12|`
⇒ ` 7/6 - x : 3/4 = 1/12`
`x : 3/4 = 7/6 - 1/12`
`x : 3/4 = 13/12`
`x = 13/12 . 3/4`
`x = 13/16`
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`c) 1/2 x - 3/5 - 2/3 x = 0`
`( 1/2 - 2/3) x - 3/5 = 0`
`-1/6 x = 0 + 3/5`
`-1/6 x = 3/5`
`x = 3/5 : (-1/6)`
`x = -18/5`
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`d) 3 . ( 2-x )+ 5( x - 1) = 0`
`3 . 2 - 3x + 5x - 5.1 = 0`
`6 - 3x + 5x - 5 = 0`
`( 6 - 5) - ( 3x - 5x) = 0`
`1 - (-2x) = 0`
`(-2x) = 1 - 0`
`-2x = 1`
`x = 1 : (-2)`
`x = -1/2`
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`e) ( x - 2) ( 3/4 x + 1) = 0`
⇒ `x - 2 = 0` hoặc `3/4 x + 1 = 0`
`x = 0 + 2` hoặc `3/4 x = 0 - 1`
`x = 2` hoặc `3/4x = -1`
`x = 2` hoặc `x = -1 : 3/4`
`x = 2` hoặc `x =-4/3`
Vậy `x∈ { 2 ; -4/3}`
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`f) ( x - 1/2)^2 - 1 = 7/9`
`( x - 1/2)^2 = 7/9 + 1`
`( x -1/2)^2 = 16/9`
`( x - 1/2)^2 = (+-4/3)^2`
⇒ `x - 1/2 = 4/3` hoặc `x - 1/2 = -4/3`
`x = 4/3 + 1/2` hoặc `x = -4/3 + 1/2`
`x = 11/6` hoặc `x = -5/6`
Vậy `x∈ {11/6 ; -5/6}`
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