Hey, just replace the `x` digit with the roots and do the problm ............
you will get it

One root is 2+√-3, one other root is 2-√-3.
Continuing with above, [x - (2+√-3)] and [x - 2-√-3)] are two factors of the given equation. Divide the given equation with expression [x-(2+√-3)]x[x-(2-√-3)]. You will get a resultant quadratic equation. Solve this quadratic equation for other roots.