The solutions to F(X) = X^3 - 3*B*X^2 + C*X + D = 0 are
B - K * cubert(F(B)/2 + R) - K^2 * cubert(F(B)/2 - R)
where R = sqrt((F(B)/2)^2 + (F'(B)/3)^3)
and K is one of the three cube roots of 1:
1, (-1+sqrt(-3))/2, (-1-sqrt(-3))/2.
The above
formula was stolen from
HAKMEM.