Basic Concepts The failure rate function is defined as z(t)）=1im Pr(t<T≤t+△t)川T>t △1→0 △t f(t) R(t) It implies that when At is small, Pr(t<T≤t+△tT>t)≈z(t)△t. The relationship between (t)and R(t): R0=exp(-人zwd CLGO System Engineering by J.J.Gao 12+ - System Engineering by J. J. Gao 12 Basic Concepts