The open loop transfer function of a unity feedback control system is
\(G\left( s \right) = \frac{{20\;k{s^3}}}{{{s^4} + 5{s^2} + 10s + 15}}\;\)
The range of k such that the closed loop system is unstable is ____1
k < 0.1
2
k > 0.1
3
unstable for any value of k
4
stable for any value of k