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Initial value problem using Laplace Transform

I have to solve the IVP: $$\begin{cases} y''+by'-cy=1\\ y(0)=y_0\\ y'(0)=y'_0 \end{cases}$$

Suppose $$Y(s)=\frac{s^2+2s+1}{s^3+3s^2+2s}$$

We have to find $b,c,y_0$ and $y'_0$

I have found that: $$(s^2+s+1)Y(s)-(s+1)y_0-y'_0=1/s$$

How do I proceed further

Robert Z's user avatar

2 Answers 2

According to the given ODE $y''+by'-cy=1$ , your last line should be $$(s^2+bs-c)Y(s)-(s+b)y_0-y'_0=1/s$$ which implies $$Y(s)=\frac{y_0s^2+(by_0+y'_0)s+1}{s^3+bs^2-cs}.$$ Now, by comparing it with $Y(s)=\frac{s^2+2s+1}{s^3+3s^2+2s}$ , we are able to find $b$ , $c$ , $y_0$ and $y'_0$ easily: $$b=3,c=-2, y_0=1, y'_0=-1.$$

You have that the Laplace transform of the solution $y(t) $ is $Y(s) $ . So the inverse Laplace transform of $Y(s) $ gives us the solution $y(t) =\frac{e^{-2t}+1}{2}$ . From this we can calculate $y(0)=1$ and $y'(0) =-1$ . Now sustitute the expression of $y(t)$ in the equation and you'll get $$e^{-2t}(4-2b+c) -(2+c) =0.$$ Since $e^{-2t}$ and $1$ are linearly independent we Have that $b=3$ and $c=-2$ .

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Laplace transform

Solve the initial value problem using Laplace transforms. y"+y=f(t) , y(0)=0 , y'(0)=1

Lennie Carroll

Lennie Carroll

Answered question

Solve the initial value problem using Laplace transforms. y " + y = f ( t ) , y ( 0 ) = 0 , y ′ ( 0 ) = 1 Here f ( t ) = { 0 0 ≤ t < 3 π 1 t ≥ 3 π

Answer & Explanation

Arnold Odonnell

Arnold Odonnell

Skilled 2021-09-07 Added 109 answers

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Browse Course Material

Course info, instructors.

  • Prof. Arthur Mattuck
  • Prof. Haynes Miller
  • Dr. Jeremy Orloff
  • Dr. John Lewis

Departments

  • Mathematics

As Taught In

  • Mathematics Differential Equations Linear Algebra

Learning Resource Types

Differential equations, laplace transform: solving initial value problems.

« Previous | Next »

Session Overview

Session activities.

Read the course notes:

  • Laplace Transform: Solving Initial Value Problems: Introduction (PDF)
  • Laplace Transform Table (PDF)
  • Table Entries: Derivative Rules (PDF)
  • Precise Definition of Laplace Inverse (PDF)
  • Laplace: Solving Initial Value Problems (PDF)
  • IVP’s and t-translation (PDF)
  • IVP’s: Longer Examples (PDF)

Watch the problem solving video:

  • Laplace: Solving ODE’s

Complete the practice problems:

  • Practice Problems 29 (PDF)
  • Practice Problems 29 Solutions (PDF)

Check Yourself

Complete the problem sets:

Problem Set Part I Problems (PDF)

Problem Set Part I Solutions (PDF)

Problem Set Part II Problems (PDF)

Problem Set Part II Solutions (PDF)

MIT Open Learning

VIDEO

  1. Inverse Laplace Transform

  2. Laplace Transforms using Derived Formulas Part 1

  3. Application of Laplace Transforms to Differential Equations-1

  4. Euler's Method-Numerical technique to solve Initial Value Problem!

  5. laplace problems _part 3

  6. Euler's Modified Method-Numerical technique to solve Initial Value Problem!

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