Laplace Transform With Initial Values

In summary, the conversation discusses the use of Laplace transform to solve an initial value problem. It involves manipulating equations and finding the inverse Laplace of a given expression. The final result is a function of s that can be broken down into two parts, one involving s^2 and the other involving a constant. The conversation ends with a request for assistance in solving the remaining part of the problem.
  • #1
diffeqnoob
14
0
Okay, I know this is alot... but I am stuck, so here goes...

Use the method of Laplace transform to solve the initial value problem

[tex]y''+3ty'-6y=0, y(0) = 1, y'(0) = 0[/tex]
[tex]L\{y'' + 3ty' - 6y\} = L\{0\}[/tex]
[tex]s^{2}Y(s) - sy(0) - y'(0) + 3L\{ty'\} - 6Y(s) = 0[/tex]
[tex]s^{2}Y(s) - s(1) - 0 - \frac{d}{ds}\left(3 L\{ty'\}\right) -6Y(s) = 0[/tex]

Now to resolve the [tex]- \frac{d}{ds}\left(3 L\{ty'\}\right)[/tex]
[tex]= - \frac{d}{ds}\left(3 L\{ty'\}\right)[/tex]

[tex]= - \frac{d}{ds}3 \left(sY(s) - y(0)\right)[/tex]

[tex]= -3sY'(s) - 3Y(s)[/tex]


Plugging it back into the eq we now have

[tex]s^{2}Y(s) - s - 3sY'(s) - 3Y(s) - 6Y(s) = 0[/tex]

[tex]-3sY'(s) + (s^{2}-9)Y(s) - s = 0[/tex]

[tex]Y'(s) + \left(-\frac{s}{3} + \frac{3}{s}\right)Y(s) = -\frac{1}{3}[/tex]

[tex]\mu = e^{\int\left(-\frac{s}{3} + \frac{3}{s}\right)ds}[/tex]

[tex]\mu = e^{\left(-\frac{s^{2}}{6} + ln(s^{3})\right)}[/tex]

[tex]\mu = s^{3}e^{-\left(\frac s^{2}{6}\right)}[/tex]

[tex]\int\left(\frac{d}{ds}(s^{3}e^{-\left(\frac s^{2}{6}\right)}Y(s)\right) = \int-\left(\frac{1}{3}\right)s^{3}e^{-\left(\frac s^{2}{6}\right)} ds[/tex]

[tex]s^{3}e^{-\left(\frac s^{2}{6}\right)}Y(s) = \int-\left(\frac{1}{3}\right)s^{3}e^{-\left(\frac s^{2}{6}\right)} ds[/tex]


RIGHT SIDE
[tex]=\left(\frac{1}{3}\right)(-3(s^{2}+6)e^{-\left(\frac{s^2}{6}\right)[/tex]

[tex]=(s^2+6)e^{-\left(\frac{s^2}{6}\right) + A[/tex]

[tex]Y(s)=\frac{(s^2+6)}{s^{3}} + \frac{A e^ \frac{s^2}{6}}{s^{3}}[/tex]

[tex] Limit as s \rightarrow \infty Y(s) = 0 therefore A = 0[/tex]

[tex]Y(s) = \frac{s^2+6}{s^3}[/tex]



Break down the Inverse Laplace
[tex]L^{-1}\{\frac{s^2+6}{s^3}\}[/tex]

[tex]=L^{-1}\{\frac{s^2}{s^3}\} + L^{-1}{\frac{6}{s^3}\}[/tex]

[tex]=L^{-1}\{\frac{1}{s}\} + L^{-1}{\frac{6}{s^3}\}[/tex]

[tex]= 1 + ? [/tex]


This is where I get lost... I don't know how to do the other side... Please help.
 
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  • #2
Why does my LaTex look all funny?
 

1. What is the Laplace Transform?

The Laplace Transform is a mathematical tool used to solve differential equations. It transforms a function of time into a function of complex frequency, making it easier to solve certain types of differential equations.

2. What are Initial Values in the context of Laplace Transform?

Initial Values refer to the values of a function at the beginning of a given time period. In the context of Laplace Transform, initial values are used to determine the unique solution to a differential equation.

3. How is Laplace Transform used to solve initial value problems?

Laplace Transform is used to convert a differential equation into an algebraic equation, which can then be solved for the unknown function. The initial values are used to find the constants in the solution, resulting in the unique solution to the initial value problem.

4. What are the benefits of using Laplace Transform to solve initial value problems?

Laplace Transform allows for the solution of complex differential equations that may be difficult to solve using traditional methods. It also provides a unique solution to initial value problems, which may have multiple solutions using other methods.

5. Are there any limitations to using Laplace Transform for initial value problems?

One limitation of Laplace Transform is that it can only be used for linear differential equations with constant coefficients. It also requires the initial values to be known, which may not always be the case in real-world applications.

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