Understanding Power Series Solutions for Differential Equations

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SUMMARY

The discussion focuses on solving the differential equation y'' + y = x using power series methods. Participants clarify the confusion surrounding the inclusion of the term 'x' on the right-hand side of the equation. The solution involves expanding the series into two parts and grouping results by powers of x, which allows for the identification of coefficients. Key insights include the necessity of handling the non-homogeneous term effectively to derive the correct power series representation.

PREREQUISITES
  • Understanding of differential equations, specifically second-order linear equations.
  • Familiarity with power series and their convergence properties.
  • Knowledge of coefficient extraction in series expansions.
  • Basic skills in manipulating summations and series notation.
NEXT STEPS
  • Study the method of Frobenius for solving differential equations.
  • Learn about the convergence of power series and their radius of convergence.
  • Explore techniques for solving non-homogeneous differential equations.
  • Practice extracting coefficients from power series expansions in various contexts.
USEFUL FOR

Students and educators in mathematics, particularly those focusing on differential equations, as well as anyone seeking to enhance their understanding of power series solutions in applied mathematics.

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Homework Statement



Solve this equation using power series: y'' + y = x



Homework Equations



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The Attempt at a Solution



I am confused about the x on the RHS of the equation. If the equation was y'' + y = 0, I would have no problem solving it. I am just a little confused about how the x fits into the equation for cn.

if the equation were y'' + y = 0, then cn + 2 = cn/(n+1)(n+2). How does the x fit into this?
 
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You should be able to split up the series you get into three parts. One of those parts will be very short, with just a single term.

Show us what you have for your series.
 
I'm a newb and don't know how to use this website, so here goes:

SUM[ (n+2)(n+1)cn+2xn] + SUM[cnxn] = x
 
<br /> \ \ \sum_{n=0}^{\infty}{(n+2)(n+1)c_{n+2}x^n} \ \ + \ \ \sum_{n=0}^{\infty}{c_{n}x^n} \ \ = x<br />

Here it is in the non-retarded version
 
Last edited:
Try expanding your two series and then grouping the results by powers of x. Be sure to take the x on the right side into account.
 
I kind of understand what you're saying, but could you try being a little more specific? I am terrible with series.
 

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