<span>х^4-5х^2=4</span>
x^4-5x^2-4=0
x^2=t
t^2-5t-4=0
Д=25-4*1*(-4)=25-16=9
t=5+3/2=8/2=4
t=5-3/2=2/2=1
x^2=4 x=-2, x=2
x^2=1 x=-1, x=1