Troubleshooting Reduction of Order Equations: Where Did I Go Wrong?

  • Thread starter Destroxia
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In summary, the conversation is about solving a differential equation using reduction of order. The attempt at a solution involved substituting a second solution of the form ysub2(t) = v(t)*ysub1(t) into the differential equation, but there was an error in the algebra. After correcting the mistake, the correct solution was found.
  • #1
Destroxia
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Homework Statement


t^2*y^'' -t(t+2)y^' + (t+2)y=0 , t>0; ysub1(t) = t

Homework Equations


Reduction of order:

A second solution is assumed to be of the form:

ysub2(t) = v(t)*ysub1(t)

The Attempt at a Solution



work.jpg


So, the algebra in the first part of the process seemed to be correct, as it canceled out all the "v" terms and left only derivatives of v. The problem seems to happen somewhere around when I turn it into a first order linear equation and attempt to multiply through by an integrating factor. As far as I, and a CAS are concerned, that integral at the end is not possible to take. This leaves the assumption that I completely goofed up my integrating factor. Where could I have gone wrong?
 
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  • #2
RyanTAsher said:

Homework Statement


t^2*y^'' -t(t+2)y^' + (t+2)y=0 , t>0; ysub1(t) = t

Homework Equations


Reduction of order:

A second solution is assumed to be of the form:

ysub2(t) = v(t)*ysub1(t)

The Attempt at a Solution



work.jpg


So, the algebra in the first part of the process seemed to be correct, as it canceled out all the "v" terms and left only derivatives of v.
I don't think so. After substituting y2(t) = tv into the differential equation, and simplifying, I ended up with this equation:
##t^3v'' - t^3v' = 0##, which is pretty easy to solve.

I'm pretty confident that this is correct, as I went ahead to find ##y_2## and found that it satisfied the diff. eqn.

RyanTAsher said:
The problem seems to happen somewhere around when I turn it into a first order linear equation and attempt to multiply through by an integrating factor. As far as I, and a CAS are concerned, that integral at the end is not possible to take. This leaves the assumption that I completely goofed up my integrating factor. Where could I have gone wrong?
 
  • #3
Okay, I re-did all my algebra and I made the mistake somewhere distributing in the middle term. Thank you for your help.
 

What is the "Reduction of Order Equation" and when is it used?

The "Reduction of Order Equation" is a mathematical technique used in differential equations to reduce the order of a second order differential equation to a first order differential equation. It is typically used when solving linear, homogeneous differential equations with constant coefficients.

How does the "Reduction of Order Equation" work?

The "Reduction of Order Equation" works by substituting a new variable, u, for the dependent variable in the original second order differential equation. This reduces the equation to a first order differential equation, which can then be solved using standard techniques.

What are the steps involved in using the "Reduction of Order Equation"?

The steps involved in using the "Reduction of Order Equation" are as follows:

  1. Identify the dependent variable, y, and its derivatives in the original second order differential equation.
  2. Substitute u = y' into the equation, and rewrite it in terms of u and its derivatives.
  3. Integrate the equation with respect to x to eliminate the highest order derivative of u.
  4. Substitute back in the original dependent variable, y, to obtain the general solution.

What are the advantages of using the "Reduction of Order Equation"?

The main advantage of using the "Reduction of Order Equation" is that it simplifies the process of solving second order differential equations, making it easier to find a solution. It also allows for the use of standard techniques for solving first order differential equations, which can be more straightforward and familiar to many scientists.

Are there any limitations to using the "Reduction of Order Equation"?

Yes, there are some limitations to using the "Reduction of Order Equation". It can only be used for linear, homogeneous differential equations with constant coefficients, so it may not be applicable to all types of differential equations. It also requires a good understanding of integration techniques and may not be suitable for beginners in differential equations.

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