You just need to apply the formula
[tex]x_{1,2}=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}[/tex]
where [tex]a,b,c[/tex] are the coefficients of the quadratic equation
[tex]ax^2+bx+c=0[/tex]
In your case,
[tex]a=1,\quad b=-6,\quad c=2[/tex]
So, the solving formula becomes
[tex]x_{1,2}=\dfrac{6\pm\sqrt{36-8}}{2}=\dfrac{6\pm\sqrt{28}}{2}=\dfrac{6\pm2\sqrt{7}}{2}=3\pm\sqrt{7}[/tex]
