e, `2x^2-3x-5=0`
`↔(2x-5)(x+1)=0`
`↔`\(\left[ \begin{array}{l}2x-5=0\\x+1=0\end{array} \right.\)
`↔`\(\left[ \begin{array}{l}x=\dfrac{5}{2}\\x=-1\end{array} \right.\)
Vậy: `S={\frac{5}{2};-1}`
f, `x^2-6x+9=0`
`↔(x-3)^2=0`
`↔x=3`
Vậy: `S={3}`
g, `x^2+7x+12=0`
`↔(x+3)(x+4)=0`
`↔`\(\left[ \begin{array}{l}x+3=0\\x+4=0\end{array} \right.\)
`↔`\(\left[ \begin{array}{l}x=-3\\x=-4\end{array} \right.\)
Vậy: `S={-3;-4}`
