Tìm x, biết: a) 4(x^2)- 6x = 0  b) ((x + 2)^2)- x(x + 2) = 3  c) (x^2) - 7x - 18 = 0

a) \(4{x^2} - 6x = 0\)

\(2x\left( {2x - 3} \right) = 0\)

\(2x = 0\) hoặc \(2x - 3 = 0\)

\(x = 0\) hoặc \(x = \frac{3}{2}.\)

 Vậy \(x \in \left\{ {0;\,\,\frac{3}{2}} \right\}.\)

b) \({\left( {x + 2} \right)^2} - x\left( {x + 2} \right) = 3\)

\({x^2} + 4x + 4 - {x^2} - 2x - 3 = 0\)

\(2x =  - 1\)

  \(x =  - \frac{1}{2}\)

Vậy \(x =  - \frac{1}{2}.\)

c) \({x^2} - 7x - 18 = 0\)

\({x^2} - 9x + 2x - 18 = 0\)

\(x\left( {x - 9} \right) + 2\left( {x - 9} \right) = 0\)

\(\left( {x - 9} \right)\left( {x + 2} \right) = 0\)

\(x - 9 = 0\) hoặc \(x + 2 = 0\)

\(x = 9\) hoặc \(x =  - 2.\)

Vậy \(x \in \left\{ {9;\,\, - 2} \right\}.\)