Why is my particular solution not matching with the book's answer?

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Discussion Overview

The discussion revolves around finding the particular solution to a differential equation of the form t^2 y'' - t(t+2)y' = (t+2)y = 2t^3, given the homogeneous solutions y1 = t and y2 = te^t. Participants are examining discrepancies between their calculated solutions and the solution provided in a textbook.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents their calculated particular solution as -2t^2 - 2t and seeks help identifying a potential mistake, noting that the book states the solution is simply -2t^2.
  • Another participant questions whether there is an error in the original equation, suggesting that the first equality might be intended as a plus sign instead of an equals sign.
  • A later reply suggests that the participant's solution is valid, as adding a linear combination of the homogeneous solutions to the particular solution yields another acceptable particular solution.
  • Another participant proposes a form for the private solution as At^3 + Bt^2 + Ct, asserting that they arrived at the same solution as the book and encourages the original poster to try again, while noting that the C term does not get canceled.

Areas of Agreement / Disagreement

Participants express differing views on the correctness of the original calculations and the interpretation of the differential equation. There is no consensus on the source of the discrepancy between the calculated and book solutions.

Contextual Notes

There are unresolved assumptions regarding the form of the differential equation and the treatment of the homogeneous solutions in relation to the particular solution.

newtomath
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Given t^2 y'' -t(t+2)y' = (t+2)y= 2t^3 and y1= t, y2= te^t
Find the particular solution-

I ve worked the problem to [ -2t^2 -2t] by:
-t * Integral [ 2t* te^t/ t^2e^t] + te^t * Integral [ 2t^2/ t^2e^t]


whereas the book states that it is simply -2t^2. Can you guys tell me where I made my mistake, I am stumped.
 
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newtomath said:
Given t^2 y'' -t(t+2)y' = (t+2)y= 2t^3 and y1= t, y2= te^t

Is that first = supposed to be +?
 
newtomath said:
Given t^2 y'' -t(t+2)y' = (t+2)y= 2t^3 and y1= t, y2= te^t
Find the particular solution-

I ve worked the problem to [ -2t^2 -2t] by:
-t * Integral [ 2t* te^t/ t^2e^t] + te^t * Integral [ 2t^2/ t^2e^t]

whereas the book states that it is simply -2t^2. Can you guys tell me where I made my mistake, I am stumped.
To be honest, I don't completely understand this, but I'm not sure you've actually done anything wrong. You got the particular solution -2t^2-2t, and the book says -2t^2. But notice that one of the homogeneous solutions is t. If you add a linear combination of the homogeneous solutions to the particular solution, you get another equally valid particular solution. So, if -2t^2 -2t works, so does -2t^2 -2t + 2t = -2t^2.
 
Well a private solution here will be of the form:
At^3+Bt^2+Ct
where you can see quite immediately that A=0 (cause it has a term of t^4 which obviously gets nullified).

I did the calculation and got exactly as the book, try again.
PS
the C term doesn't get canceled though.
 
Last edited:

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