A unity feedback system has a nominal characteristic equation
q(s) = s3 + 3s2 + 3s + 6 = 0.
The coefficients vary as follows:
2 ≤ a2 ≤ 4, 1 ≤ a1 ≤ 4,
4 ≤ a0 ≤ 5.
Determine whether the system is stable for these uncertain coefficients.