Laplace Differential equation

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  • #1
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I have a differential equation that has to be solved with Laplace. I wish someone can provide a full answer

y'' + 4y = x , 0<=x<π
y'' + 4y = πe^-x , π<=x

Initial Conditions:
y(0)=0 y'(0)=1
 

Answers and Replies

  • #2
Integral
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Sorry we do not do that here.

Start by applying Laplace tranforms to each of the equations.
 
  • #3
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Learn this: http://tutorial.math.lamar.edu/Classes/DE/LaplaceIntro.aspx
and you will know what to do :)

also your ODE can be written using the step (Heaviside) function:

y'' + 4y = x + H[x-π](πe^(-x) - x)

H[x-π] = 0 at x<π; H[x-π] = 1 at x>=π;


Good Luck.
 
  • #4
HallsofIvy
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I have a differential equation that has to be solved with Laplace. I wish someone can provide a full answer

y'' + 4y = x , 0<=x<π
y'' + 4y = πe^-x , π<=x

Initial Conditions:
y(0)=0 y'(0)=1
No "full answer" but:
1) Solve y"+ 4y= x, 0<= x< [itex]\pi[/itex]
with initial conditions y(0)= 0, y'(0)= 1.

Evaluate the function, [itex]y_1(x)[/itex], satifying those conditions and its derivative at [itex]x= \pi[/itex] and solve
2) [itex]y''[/itex][itex]+ 4y= [/itex][itex]\pi e^{-x}[/itex]
with initial conditions [itex]y(\pi)= y_1(\pi)[/itex], [itex]y'(\pi)= y_1'(\pi)[/itex].
 
  • #5
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Where I am stuck is how to transform the right part as to write it for the proper laplace transform
How I would do it(and correct me where I am wrong)
y'' + 4y = x[u(x-0)-u(x-π)] + πe^(-x)*u(x-π)

How do you apply the Heavyside? Can you explain me your technique?
 
  • #6
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Why would you want to use a Heaviside step function? Please advise.

You need to transform the equation. What have you got so far?
 
  • #7
HallsofIvy
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I can see no good reason to use "Laplace transform". The problem is close to trivial with regular methods (find the general solution to the associated homogeneous equation and add a particular solution found by "undetermined coefficients".
 

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