Solving a Second Order Differential Equation: Help Needed

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Discussion Overview

The discussion revolves around the second order differential equation y'' + y(x^2 + e^x) = 0. Participants explore the challenges of solving this equation, particularly due to the presence of both polynomial and transcendental functions in the coefficients. The conversation includes hints, proposed methods, and expressions of uncertainty regarding analytical solutions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant expresses uncertainty about a potential typo in the problem statement, questioning the presence of both dependent and independent variables.
  • Another participant doubts that an analytical method exists to find the two solutions due to the non-constant coefficients.
  • A participant suggests that series solutions might be the only viable approach, noting that many introductory texts cover this method.
  • One participant shares their experience using numerical methods (NDSolve) with arbitrary initial conditions, indicating that while not analytically derived, the results provide a starting point for understanding the problem.
  • Another participant reiterates the suggestion of using series methods, expressing frustration about the lack of discussion on this topic in the textbook.
  • A final suggestion encourages checking elementary differential equations resources for more information on series methods.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method to solve the differential equation. There are multiple competing views regarding the feasibility of analytical solutions and the appropriate techniques to apply.

Contextual Notes

Participants note the complexity introduced by the non-constant coefficients and the absence of specific guidance in the textbook regarding series solutions. There is also an acknowledgment of the limitations of the methods discussed, particularly in the context of a first course in differential equations.

EvLer
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Hello, not sure if it's a typo in the book but I can't work this out:

y'' + y(x^2 + e^x) = 0;

It's second order but both dependent and independent variables are present, and i am stuck.
You don't have to solve it for me entirely, a hint would be great.

Thanks in advance.
 
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The coeff are not constant and one is a polynomial and the other a transcendental function.I doubt one can find an analytical method to find the 2 solutions.

Daniel.
 
Are you saying that there's a typo in the problem?
(it's a first Diff Eq course)
 
Not necessarily. Many first course d.e. texts introduce "series solutions" but that's the only way I see to do this.
 
When in doubt guess. I ain't proud. I used NDSolve with initial conditions (just out of thin air) of y(0)=1,y'(0)=0. The results are below. I know it's not a solution but at least it's the start of a handle. :smile:

Edit: Wait a minute. That IS a solution. I mean it's not an analytically derived one. :smile:
 

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Last edited:
HallsofIvy said:
Not necessarily. Many first course d.e. texts introduce "series solutions" but that's the only way I see to do this.
I'm sure it's somehow deducible with series, but unfortunately the book does not discuss that anywhere, i guess i'll have to google. I wish the book or the instructor would give more of "and why do we do this?" rather than "here's how: plug and chug".

Thanks everyone.
 
Last edited:
You should use series method to solve this diff eq.
It's hard to explain the method in this tiny box(!). I suggest to check out an elemantary diff eq book and read the chapter about the series method.
 

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