Chapter 5.9, Problem 13P

In each of Problems $12$ through $15$, use the Routh criterion to find the range of $K$ for which all the poles of the transfer functions are in the left half of the complex plane. Then use a computer program to verify your answers by plotting the poles in the s-plane for various values of $K$.

$\frac{K\left(s+1\right)\left(s+2\right)}{s^3+4s^2+6s+4+K}$