Tìm x biết: a) 4{x^2} - 6x = 0.
Giải thích
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 \(x \in \left\{ {9;\,\, - 2} \right\}.\) |