Efficient Laplace Transform for t*cos(3t) and e^(2t)sin(4t) Functions

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Discussion Overview

The discussion revolves around finding the Laplace transforms of the functions \(t \cos(3t)\) and \(e^{2t} \sin(4t)\), including the combination of these transforms. Participants explore the correctness of their calculations and the necessary steps for combining results.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant presents the Laplace transform for \(t \cos(3t)\) and claims to have derived the transforms for \(g(t)\) and \(h(t)\) as well.
  • Another participant agrees with the first transform but suggests that the second transform is incorrect due to a missing multiplication factor.
  • A third participant proposes a corrected form for the third transform and expresses uncertainty about whether to combine the results.
  • A later reply clarifies that combining the transforms is only necessary if explicitly requested in the problem statement.

Areas of Agreement / Disagreement

Participants generally agree on the correctness of the first Laplace transform, while there is disagreement regarding the second and third transforms, with multiple competing views on their accuracy. The discussion remains unresolved regarding the necessity of combining the transforms.

Contextual Notes

Some assumptions about the transforms and their combinations are not explicitly stated, and there are unresolved mathematical steps in the derivations presented by participants.

Lucy77
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Find laplace transfom (t-1)cos3t + e^(2t)sin4t

f(t) = t*cos(3*t)
g(t) = -cos(3*t)
h(t) = e2*t*sin(4*t)


int e^(-st) * t* cos(3*t)dt = s^(2)-9/(s^(2)+9)^2
g(t)= -1/(s^2+9)
h(t)= (s-2)/(s-2)^2 +16

am I done and right? Thanks
 
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The first one is right. The second one is close (you forgot to multiply by 9). The third one looks way off.

In general, L{ebtsin(at)}=a/[(s-b)2+a2]
 
Thanks,

The third one should be 4/(s-2)^2+16. Do I have to combine all of these. Am unsure about that part.

Thanks
 
You only have to combine them if the problem says so.

Did they ask you to find L{f(t)+g(t)+h(t)}?

If not, then you can leave them separate.
 

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