`a, 2/3x - 1/2x = -5/12`
$\Leftrightarrow$ `1/6x = -5/12`
$\Leftrightarrow$ `x = -5/12 : 1/6`
$\Leftrightarrow$ `x = -5/2`
$\text{Vậy}$ `x = -5/2`
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`b, 3/{4 . (x - 8)} = 5/{7.(14 - 7/2)}`
$\Leftrightarrow$ `3/{4x - 32} = 5/{7 . 21/2}`
$\Leftrightarrow$ `3/{4x - 32} = 5/{147/2}`
$\Leftrightarrow$ `3 . 147/2 = 5 . (4x - 32)`
$\Leftrightarrow$ `5 . (4x - 32) = 3 . 147/2`
$\Leftrightarrow$ `5 . (4x - 32) = 441/2`
$\Leftrightarrow$ `(4x - 32) = 441/2 : 5`
$\Leftrightarrow$ `4x - 32 = 441/10`
$\Leftrightarrow$ `4x = 441/10 + 32`
$\Leftrightarrow$ `4x = 761/10`
$\Leftrightarrow$ `x = 761/10 : 4`
$\Leftrightarrow$ `x = 761/40`
$\text{Vậy}$ `x = 761/40`
