<span> (а^2+4)^2-16a^2=a^4+8a^2+16-16a^2=a^4-8a^2+16=(a^2-4)^2</span>
x^3=t
9x^-6x+1=0
(3х-1)^2=0
3x-1=0
3x=1
x=1/3
x=0.3