Routh's Criterion 

Routh's Criterion
-1 
-1  -1   
3.5  2.5  -1 
-2.42857142857143  -0.428571428571429 
1.88235294117647  -1 
-1.71875 
-1 
The polynomial p(x) = x6 + 2x5 + 3x - x3 + 2x2 - x - 1 has three roots with positive real parts.


Reference: K. Ogata, Modern Control Engineering, pp. 253-257.