# Finding the time constant

1. Sep 23, 2012

### Rombus

1. The problem statement, all variables and given/known data
Find the time constant
$x(t)=4 e^{-4t} u(t)$

2. Relevant equations
$\tau = \frac{1}{\lambda}$

3. The attempt at a solution
$\tau = \frac{1}{\lambda}= \frac{1}{4} = .25$

I know the unit step is shifting the start of the decay function to zero, but I'm not sure how or if this can affect the time constant. So my question is how does the unit step affect the time constant?

2. Sep 23, 2012

### Ray Vickson

It has no effect. Just recall the definition of time constant.

RGV