# Need someone to check LT

• Nov 9th 2010, 08:22 AM
maliZeleni
Need someone to check LT
i have signal as shown on the attached image, and i need to introduce it analytically and apply Laplace transformation on it...

signal is :
Attachment 19646

and i have done this :D

$\displaystyle f(t) = 10\cdot t \cdot u(t) - 20 \cdot (t-10) \cdot u(t-10) +10\cdot (t-20) \cdot u(t-20)$

that's as far as writting it analytically... (is this correct ? )

now with LT ...

$\displaystyle F(S)= 10 S \frac {1}{S} -20e^{-10S} \frac {1}{S} + 10 e^{-20S} \frac {1}{S} =$

$=10 - 20 e^{-10S}\frac {1}{S} + 10 e^{-20S}\frac {1}{S}$

P.S. sorry for bad image :D:D:D:D
• Nov 9th 2010, 08:27 AM
Ackbeet
You need to crunch your f(t) down a bit. The correct formula is yours divided by 10. How does that change your LT?
• Nov 9th 2010, 08:34 AM
maliZeleni
Quote:

Originally Posted by Ackbeet
You need to crunch your f(t) down a bit. The correct formula is yours divided by 10. How does that change your LT?

aaaah, my bad... it's not 10t.....

i get :

$f(t) = t u(t) - 2 (t-10) u(t-10) + (t-20)u(t-20)$

so LT is

$F(S) = 1 - 2e^{-10s} \frac {1}{s} + e^{-20s} \frac {1}{s}$

is that it ? :D:D:D
• Nov 9th 2010, 08:39 AM
Ackbeet
Here's a way to check it for yourself. WolframAlpha is a great website.
• Nov 9th 2010, 09:01 AM
maliZeleni
Quote:

Originally Posted by Ackbeet
Here's a way to check it for yourself. WolframAlpha is a great website.

thank you :D
• Nov 9th 2010, 09:02 AM
Ackbeet
You're welcome. Have a good one!