[tex]\displaystyle 3^{x^2+3}=3\times 3^{3x}\Leftrightarrow 3^{x^2+3}=3^{3x+1}\Leftrightarrow x^2+3=3x+1\Leftrightarrow\\
x^2-3x+2=0\\ \\
\left \{ {{x_1+x_2=3} \atop {x_1\times x_2=2}} \right. \Leftrightarrow \left \{ {{x_1=2} \atop {x_2=1}} \right. \\ \\ \\
S=\{2;1\}[/tex]
