A system with transfer function \(G\left( s \right) = \frac{1}{{\left( {s + 1} \right)\left( {s + a} \right)}},\;a > 0\) is subjected to an input 5 cos 3t. The steady-state output of the system is \(\frac{1}{{\sqrt {10} }}\cos \left( {3t - 1.892} \right)\). The value of a is
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