Hello!
How can I solve it?
$\displaystyle (a^4 + a^2 + 1) $
Let $\displaystyle u = a^2$ so $\displaystyle a^4+a^2+1 = u^2+u+1$
If it can be factorised the discriminant will be a square number: $\displaystyle \Delta = b^2-4ac = 1^2- 4 \times 1 \times 1 = 1-4 = -3$. Since the discriminant is not a square number it cannot be factorised. In addition you will have complex solutions.
Use the quadratic formula to find u and then find a using the fact that $\displaystyle a = \pm \sqrt{u}$