[tex]x^4-5x^2+4=0,~~t=x^2~\land~t\geq 0\\t^2-5t+4=0\\\Delta=25-4*4=9\\\sqrt{\Delta} =3\\t_1=\frac{5-3}{2} =1>0\\t_2=\frac{5+3}{2} =4>0\\\\t=1~\vee~t=4\\x^2=1~\vee~x^2=4\\x=1~\vee~x=-1~\vee~x=2~\vee~x=-2[/tex]
Pozdrawiam.
