Giải p t `5x^2 - 9x = 2 `

` 5x^2 - 9x = 2 `

` ⇔ 5x² - 9x - 2 = 0 `

` ⇔ 5x² + x - 10x - 2 = 0 `

` ⇔ ( 5x² + x ) - ( 10x + 2 ) = 0 `

` ⇔ x ( 5x + 1 ) - 2 ( 5x + 1 ) = 0 `

` ⇔ ( 5x + 1 ) ( x - 2 ) = 0 `

` ⇔ ` $\left[\begin{matrix} 5x + 1 = 0 \\ x - 2 = 0 \end{matrix}\right.$

` ⇔ ` $\left[\begin{matrix} 5x = -1 \\ x = 0 + 2 \end{matrix}\right.$

` ⇔ ` $\left[\begin{matrix} x = \dfrac{-1}{5}  \\ x = 2 \end{matrix}\right.$

Vậy ` S = { [ -1 ] / 5 ; 2 } `