I'm trying to take the derivative of: $$\frac{-1}{6}(e^{-3t}-1) u(t)$$
The $u(t)$ is the step response. So the answer I get is by just doing product rule: $$\frac{1}{2}e^{-3t}u(t)-\frac{1}{6}e^{-3t}\delta(t)$$ but wolfram gets a different answer.
Why does: $-\frac{1}{6}e^{-3t}\delta(t)$ goes to $0$?