[tex]M(x)=x^{4}+x^{2}+6[/tex]
[tex]=x^{4}+\frac{1}{2}x^{2}+\frac{1}{2}x^{2}+\frac{1}{4}+\frac{23}{4}[/tex]
[tex]=x^{2}(x^{2}+\frac{1}{2})+\frac{1}{2}(x^{2}+\frac{1}{2})+\frac{23}{4}[/tex]
[tex]=(x^{2}+\frac{1}{2}^2+\frac{23}{4}> 0\forall x[/tex]
Vậy [TEX]M(x)[/TEX] vô nghiệm