MTTFS
This quantity, MTTF (θ), can be obtained from equation (4.8a) using the relationship:
which, because μ>>λ, can to a good approximation, be written in the form:
However, if μ=0, equation (4.11a) becomes 
 | This result can also be obtained by integrating the right-hand side of equation 2.12 from t=0 to t=∞. |