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laplace transform problem...i am confused...

A

AznMaverick

Platinum Member
i'm sorry i keep doing this, but it's just that i don't get much of this material because my professor is FOB and very bad at explaining everything. i've read the book and tried working the prof's examples and still no luck. i'm here as a last resort. we have a problem f(t)=Acos(wt+theta)*u(t) and we have to find the Laplaace Transform of this.

do i integrate Acos(wt + Theta) * e^(-st) bounds 0 < t < infinity...or something else? i'm very confused...any help is welcome
Thanks.
 
Originally posted by: AznMaverick
i'm sorry i keep doing this, but it's just that i don't get much of this material because my professor is FOB and very bad at explaining everything. i've read the book and tried working the prof's examples and still no luck. i'm here as a last resort. we have a problem f(t)=Acos(wt+theta)*u(t) and we have to find the Laplaace Transform of this.

do i integrate Acos(wt + Theta) * e^(-st) bounds 0 < t < infinity...or something else? i'm very confused...any help is welcome
Thanks.
Click to expand...

Yeah... in the general sense, you normally integreate from negative infinity to postive infinity, but your function has a step function in it u(t). So for values less than zero, your function is zero. So you can just start at zero to positive infinity.


<edit> At the advanced level, you just don't care.. and just look up tables... heh
 
e^iwt=cos(wt)+isin(wt) e^-(iwt)=cos(wt)-i*sin(wt) figure out what cos(wt) in terms of e is, plug it in, and integrate. you should get something like this L[cos(wt)]=s/(s^2+w^2), of course it might not heh.
 
I learned all that at one time in college.

I have never used it for anything since.. and have forgotten it all.
 
Originally posted by: spacelord
I learned all that at one time in college.

I have never used it for anything since.. and have forgotten it all.
Click to expand...

please don't tell me i am learning all this stuff for nothing...ugh! it is currently driving me nutz0rz
 
Learned it in college - Have never used it since (30 years)

If you have problems understanding something from the prof, go ask a grad student or any other prof.
 
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