# Thread: Help me determine the Laplace Transform and the ROC?

2. ## Re: Help me determine the Laplace Transform and the ROC?

Hi essedra!

The Laplace transform is given by:

$\mathcal{L}_t[\chi(t)](s) = \int_0^\infty \chi(t) e^{-st} dt$

Is this also the Laplace transform you are supposed to calculate?
I ask since it is a bit strange to see u(t+3) as part of the function...

Can you evaluate that integral?

3. ## Re: Help me determine the Laplace Transform and the ROC?

WolframAlpha to the rescue.

4. ## Re: Help me determine the Laplace Transform and the ROC?

Originally Posted by Ackbeet
WolframAlpha to the rescue.
Aww... you take all the fun out of it!

My problem with u(t+3) is that it is the Heaviside step function that "steps" at t=-3, which is out of bounds for the integral.
In other words, it does not do anything!?

5. ## Re: Help me determine the Laplace Transform and the ROC?

Originally Posted by ILikeSerena
Aww... you take all the fun out of it!

My problem with u(t+3) is that it is the Heaviside step function that "steps" at t=-3, which is out of bounds for the integral.
In other words, it does not do anything!?
I suppose that's true of the standard one-sided LT.