The state equation of an LTI system is \(\dot X\left( t \right) = \left[ {\begin{array}{*{20}{c}} 0&1\\ { - 2}&{ - 1} \end{array}} \right]X + \left[ {\begin{array}{*{20}{c}} 0&1\\ 1&0 \end{array}} \right]U\). The closed-loop poles of the system are 'a' and 'b'. Then a + b = ______
Enter numerical value using the virtual keypad. Round off where necessary.