Solution
= Solution
Writing $\pi=(\pi_1,\pi_2)$, the equations $\pi Q=0$ and $\pi_1+\pi_2=1$ give
$$
\boxed{\pi=\left(\frac\lambda{s},\frac\mu{s}\right)}.
$$
This is the <invariant distribution of a continuous-time Markov chain>[invariant distribution]. Since $e^{-st}\to0$, both rows of $P(t)$ converge to $\pi$, directly verifying convergence to equilibrium.