Translations:Analog linear time-invariant systems/2/en

${\begin{aligned}\int \limits _{-\infty }^{\infty }{{\delta }_{\varepsilon }}\left(t\right)dt{=1,\ }{\mathop {\lim } _{\varepsilon \rightarrow \infty }\ }\int \limits _{\infty }^{-\infty }{{\delta }_{\varepsilon }}\left(t\right)f\left(t\right)dt=f\left(0\right),\end{aligned}}$

(17)