Tìm x biết: a) 6x^2 - 10 x = 0 b) ( x+3)^ 2 - x ( x+ 3) =8

a) \(6{x^2} - 10x = 0\)

\(2x\left( {3x - 5} \right) = 0\)

\(2x = 0\) hoặc \(3x - 5 = 0\)

\(x = 0\) hoặc \(x = \frac{5}{3}.\)

 Vậy \(x \in \left\{ {0;\,\,\frac{5}{3}} \right\}.\)

b) \({\left( {x + 3} \right)^2} - x\left( {x + 3} \right) & = 8\)

\({x^2} + 6x + 9 - {x^2} - 3x - 8 = 0\)

\(3x = - 1\)

\(x = - \frac{1}{3}\)

Vậy \(x = - \frac{1}{3}.\)

c) \({x^2} - 5x - 14 = 0\)

\({x^2} - 7x + 2x - 14 = 0\)

\(x\left( {x - 7} \right) + 2\left( {x - 7} \right) = 0\)

\(\left( {x - 7} \right)\left( {x + 2} \right) = 0\)

\(x - 7 = 0\) hoặc \(x + 2 = 0\)

\(x = 7\) hoặc \(x = - 2.\)

Vậy \(x \in \left\{ {7;\,\, - 2} \right\}.\)