Tìm x , biết: (a) 3 − 4 x/− 3 = x − 2/5 ; (b) 12 x^2 − 4 x ( 3 x + 1 ) = x − 15 .

a) \(\frac{{3 - 4x}}{{ - 3}} = \frac{{x - 2}}{5}\)

\(5\left( {3 - 4x} \right) = - 3\left( {x - 2} \right)\)

\(15 - 20x = - 3x + 6\)

\( - 17x = - 9\)

\(x = \frac{9}{{17}}\).

Vậy \(x = \frac{9}{{17}}\).

b) \[12{x^2} - 4x\left( {3x + 1} \right) = x - 15\]

\(12{x^2} - 12{x^2} - 4x - x = - 15\)

\( - 5x = - 15\)

\(x = 3\)

Vậy \(x = 3\).