Đáp án:
`y^2 - y = 3/4`
`<=> y^2 - y - 3/4 = 0`
`<=> y^2 - 3/2 y + 1/2 y- 3/4 = 0`
`<=> y ( y - 3/2 ) + 1/2 ( y - 3/2 ) =0`
`<=> ( y + 1/2 )( y - 3/2 )=0`
`<=>` $\left[\begin{matrix} y + \dfrac{1}{2} = 0\\ y - \dfrac{3}{2} = 0\end{matrix}\right.$
`<=>` $\left[\begin{matrix} y= \dfrac{-1}{2}\\ y = \dfrac{3}{2}\end{matrix}\right.$
Vậy `S={ -1/2 ; 3/2}`
