I admit this is not an easy problem.
Suppose are roots such that . This means .
Thus we can write .
If we let .
And since .
Thus we found
Now you can find the roots of the 2 quadratic factors yourself.
Let the two roots be: .Solve the equation:
given that the sum of two of its roots is zero.
Subtract  - : .
. . and we have three roots: .
. . but is an exraneous root.
Hence, two of the factors are: .
Dividing , we get: .
The equation becomes: .
Therefore, the roots are: .