[tex]2x^2+4=40\ \ \ \ \ |-4\\\\2x^2=36\ \ \ \ |:2\\\\x^2=18\to x=\pm\sqrt{18}\\\\x=\pm\sqrt{9\cdot2}\\\\x=\pm\sqrt9\cdot\sqrt2\\\\x=-3\sqrt2\ \vee\ x=3\sqrt2[/tex]
