# Problem 2.29, HW3, ECE301, Summer 2008

Find if each system is stable and causal.

**A**

h(t) = $ e^{-4t} u(t-2) $

u(t-2) = 1 for t >= 2 making h(t) = 0 for t < 2. The system is causal.

$ \int_{-\infty}^\infty e^{-4t} u(t-2) = /int_2^\infty e^{-4t} < \infty $. Therefore the system is stable.

This system is stable and causal.

**B**

h(t) = $ e^{-6t} u(3-t) $

u(3-t) = 1 for t<=3, making h(t) $ \neq $ for t < 0. The system is not causal.

$ \int_{-\infty}^\infty e^{-6t} u(3-t) = \int_{-\infty}^3 e^{-6t} = \infty $, therefore the system is not stable.

This system is neither causal or stable.

**E**

h(t) = $ e^{-6|t|} $

Since h(t) $ \neq $ 0 for t < 0 so the system is not causal.

$ \int_{-\infty}^\infty e^{-6|t|} = 2\int_0^\infty e^{-6t} < \infty $. This system is stable.

This system is stable but not causal.