x^4-5x^2+4=0 x^2=a
a^2-5a+4=0
D=(-5)^2-4×1×4=25-16=9=3^2
a1=5+3/2=4
a2=5-3/2=1
x^2=4
x1=2 x2=-2
x^2=1
x3=1 x=-1
x^4-5x^2+4=0 x^2=a
a^2-5a+4=0
D=(-5)^2-4×1×4=25-16=9=3^2
a1=5+3/2=4
a2=5-3/2=1
x^2=4
x1=2 x2=-2
x^2=1
x3=1 x=-1