[TEX]\frac{3\sqrt{19}}{x^3}-2x^3+\frac{25}{x}+\sqrt{19}x=0[/TEX]
[tex]\left ( x^2-\frac{1}{2}(\sqrt{19}+\sqrt{31}) \right )\left ( 2x^4+\sqrt{31}x^2-\frac{19}{2}+\frac{\sqrt{589}}{2} \right )=0[/tex]
=> [tex]x^2-\frac{1}{2}(\sqrt{19}+\sqrt{31})=0<=>x=\pm \sqrt{\frac{1}{2}(\sqrt{19}+\sqrt{31})}[/tex]
[tex]2x^4+\sqrt{31}x^2-\frac{19}{2}+\frac{\sqrt{589}}{2}=0[/tex]
[TEX]t=x^2;t\geq 0[/TEX]
=> [tex]2t^2+\sqrt{31}t-\frac{19}{2}+\frac{\sqrt{589}}{2}=0[/tex] ( cái này vô nghiệm nha tự c/m nhé )