# Inverse Laplace Transform

## Recommended Posts

Hi guys, does anybody here knows ** to do inverse Laplace?

This three problem (attached) is troubling me for the past few days..

Thank you..

BTW, If i don't answer this by April 6, 2008... my professor is gonna cancel my candidacy for graduation..

##### Share on other sites

So am I, aside from the fact that I won't graduate if I don't answer those questions..

BTW, those are from Advance Engineering Math with Numerical Methods subject...troublesome!

##### Share on other sites

woah... i'll try to browse my notes

##### Share on other sites

wuhu.. got the answer on the third problem,  but im not sure if its right.. hhaha

##### Share on other sites

got the answer on number two... hahaa!! i hope my answer is correct,  i'll try problem1, whew..  where do u study?from wt school? we take this up on differential equations.. 2 years ago.. haha,

##### Share on other sites

my answer in number 2 is..

-(1/5) + (6/5)e^(-5t)

for number 3

-(3/2)e^(t) + (1/6)e^(-t) + (4/3)e^(2t)

for number 1

i have a partial answer, but i got troubled  on one part, so i cnt gve an answer il try tom.

##### Share on other sites

In maths, answers are worthless without how you ended up with that answer. This looks interesting, I'm probably seeing this next semester. Can't wait.

##### Share on other sites

my answer in number 2 is..

-(1/5) + (6/5)e^(-5t)

for number 3

-(3/2)e^(t) + (1/6)e^(-t) + (4/3)e^(2t)

for number 1

i have a partial answer, but i got troubled  on one part, so i cnt gve an answer il try tom.

Thanks mapuamj...

i see you got an interesting input... but how did you come up with those answers?

checking on my notes.. problem 1 is solve by theorem 2 in inverse laplace transform, by which it must be in the form f(s-a), then solve its laplace..

yes i do have answer for that.. i'll post it later and my point why i still post that problem regarding i already have an answer for it...

the third problem is solve by partial fractions, but first you have to get the factor of the polynomial in the denominator.. either by synthetic division or trial and error...

considering synthetic division, i always arrive in a solutiuon that involves imaginary numbers...

and even if I use Casio FX-991 ES calculator to solve its factor, it always arrived at factors containing imaginary numbers...

But my professor says it doesn't have one, or at least the paper that he checked already has no imaginary number on it.. and it is correct..

i'll try posting the "correct" answer on number 1 and number 3.. a little later...

##### Share on other sites

here is what i was talking about a while ago..

##### Share on other sites

on number three im a little bit sure of my  answer..refer to my solution, any way where do you study??

##### Share on other sites

P.U.P. Manila, btw.. I maybe wrong but when i tried multiplying (s-1)(s-2)(s+1)

i arrived at s^3 - 2s^2 - s + 2...

but from the given problem it is s^3 + 2s^2 -s + 2

they are different in sign.. that is why i always came up with imaginary numbers...

Thanks for number two it is solve by partial fractions.. now i get it..

BTW, please save my butt on question 1 and 3..

I also arrived at factors (s-1)(s+1)(s-2).. like what i have said before when you multiply those factors, the answer is not the same as what is in the problem... puzzling...

##### Share on other sites

woa.. now i see.. haha il try again whats ur program?

##### Share on other sites

are you sure that it is a positive sign?? in s^3.<....+....>.2s^2-s +2...???

##### Share on other sites

yes i am very sure that this is the denominator in problem three;

s^3 + 2s^2 - s + 2

program? what program? by that you mean our curriculum?

if yes, then we use 2001 Curriculum....

and while you're at it.. can you please check my solution to this question.. i forgot my differential calculus already.. hehehe...

thanks a lot, you are such a big help..

##### Share on other sites

haha.. no what i mean what course are you taking up,  on your last post? what's that? laplace transform? whew forgot my differential calculus.. i take that up when i was a freshmen haha.. i'll try anyway

##### Share on other sites

ah gets. .. this is our second to the last lesson on differential equations, "transforms of derivatives" i dont knw if i cn still remember this one.. haha this was taught 2 or 3 yrs ago to us at the latter part of the term so probably im not listening..ahhaha

##### Share on other sites

@mapuamj,

I'm taking BS Mechanical Engineering...

BTW, is it possible that my professor did a typo in the sign of his problem in question number three.. no matter how i figure it out, it always comes to that s^3 + 2s^2 - s + 2 must be s^3 - 2s^2 - s + 2, what do you think?

In case that problem three is not a typo, I've search about Laplace and Inverse Laplace over the net, but i can't see a Laplace that has an imaginary function except for complex conjugate.. involving sin and cos..

If I solve the factors of s^3 + 2s^2 - s + 2, it always has an imaginary number..., that is why i have too look over the net if there are functions of laplace involving imaginary numbers...

##### Share on other sites

ah..  im not really sure, but base on may notes, thats how we solve that problem, can you consult your professor about that? i really chekd it and there's no possible way on how "i" can get the roots of that if it iss^3 + 2s^2 - s + 2 ... hehe , if you want check out my notes i'l scan it, whats ur ym?

##### Share on other sites

uhhmmm, sounds fun.. ask me bout anatomy and stuff not this.? lol.. im glad i took up nursing..

guys good luck with everything! you two sounds like genius!

##### Share on other sites

hah.. any way i know u got more note than i have hahaha.. u can solve it.. just try!

##### Share on other sites

@ ianonline wahaha im not genius, just an average one

##### Share on other sites

• CA3LE locked this topic
This topic is now closed to further replies.
×
• Forums

• #### Extras

• My Results
×
• Create New...