` x^2 - 2x -3 =0`
`<=> x^2 + x - 3x - 3=0`
`<=> x(x+1) - 3(x+1) =0`
`<=> (x-3)(x+1) =0`
`<=>` \(\left[ \begin{array}{l}x-3=0\\x+1=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=3\\x=-1\end{array} \right.\)
Vậy `S = {-1;3}`
.
`x^2 + 3x +2 =0`
`<=> x^2 + x + 2x + 2 =0`
`<=> x(x+1) + 2(x+1)=0`
`<=> (x+2)(x+1) =0`
`<=>` \(\left[ \begin{array}{l}x+2=0\\x+1=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=-2\\x=-1\end{array} \right.\)
Vậy `S = {-2;-1}`
