Question

How to find the roots of a polynomial of degree 4.

Answer 1

In this case, the factor that comes out is x=−3, so you would divide by (x+3). Repeat until you've reduced to a quadratic, and then use the quadratic formula to find the irrational coefficients (if any). Simple factorisation solves your problem. Hence the 4 roots are x=12,x=−3,x=2i and x=−2i.