1) Solving this quadratic equation by the Resolutive formula, we have:
[tex]\begin{gathered} x^2+6x\text{ +9=12} \\ x^2+6x-12+9=0 \\ x^2+6x-4=0 \\ \Delta=b^2-4ac=6^2-4(1)(-4)=36+16=52 \\ x=\frac{-6\pm\sqrt[]{52}}{2} \\ x_1=-3+\sqrt[]{13} \\ x_2=-3-\sqrt[]{13} \\ S=\mleft\lbrace-3-\sqrt[]{13},-3+\sqrt[]{13}\mright\rbrace \end{gathered}[/tex]