Finding Laplace transform of a Differential Equation

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SUMMARY

The discussion focuses on solving the initial value problem represented by the differential equation y'' - 6y' - 7y = sin(9t) with initial conditions y(0) = -4 and y'(0) = -3 using the Laplace transform. The user correctly applies the Laplace transform properties, leading to the equation Y(s) = ((9/(s²+81)) + 17)/(s² - 6s - 7). However, the user encounters issues with the homework submission system indicating an error in their solution, specifically regarding the inverse Laplace transform of y''. The need to verify the Laplace transform calculations is emphasized.

PREREQUISITES
  • Understanding of Laplace transforms and their properties
  • Familiarity with solving differential equations
  • Knowledge of initial value problems
  • Experience with partial fraction decomposition
NEXT STEPS
  • Review the properties of the Laplace transform, particularly for derivatives
  • Practice solving initial value problems using the Laplace transform
  • Learn about the inverse Laplace transform techniques
  • Explore partial fraction decomposition in the context of Laplace transforms
USEFUL FOR

Students studying differential equations, particularly those working with initial value problems and Laplace transforms, as well as educators looking for examples of common pitfalls in homework submissions.

TheC0bbler
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Homework Statement


Consider the following initial value problem:

y''-6y'-7y=sin(9t)

y(0)=-4, y'(0)=-3

I need to solve for L[y(t)]

Homework Equations


The Attempt at a Solution



Here are the steps I've taken to solve it:

L(y'')-6L(y')-7L(y)=L(sin(9t))

s2L(y)-(-4)-(-3)-6(sL(y)-(-4))-7L(y)=9/(s2+81)

L(y)(s2-6s-7)-17=9/(s2+81)

L(y)(s2-6s-7)=9/(s2+81)+17

Y(s) =((9/(s2+81))+17)/(s2-6s-7)

I've simplified it with partial fractions as well but either way when I enter it into my homework page it says it's wrong.
 
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Not sure if the work is correct but you have to inverse the Laplace transform at the to solve.
 
Recheck your Laplace transform of y''.
 

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