Solving Legendre's Equation | Recurrence Relation

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SUMMARY

The discussion focuses on deriving the recurrence relation for the coefficients \( a_r \) in the series solution of Legendre's equation, specifically the equation \( (1-x^2)y'' - 2xy' + k(k+1)y = 0 \). The established recurrence relation is \( (n+2)(n+1)a_{n+2} - a_n(n(n+1) - k(k+1)) = 0 \). It is concluded that if \( k \) is a positive integer, then \( a_{k+2} = 0 \), indicating that the solution is a polynomial of degree \( k \). The discussion also touches on the need to express coefficients \( a_2, a_3, \) and \( a_4 \) in terms of \( a_0 \) and \( a_1 \) and the potential use of mathematical induction to prove a general form for \( a_n \).

PREREQUISITES
  • Understanding of Legendre's equation and its significance in mathematical physics.
  • Familiarity with recurrence relations and their applications in series solutions.
  • Basic knowledge of polynomial functions and their properties.
  • Introduction to mathematical induction as a proof technique.
NEXT STEPS
  • Study the derivation of recurrence relations in differential equations.
  • Learn about the properties of Legendre polynomials and their applications.
  • Explore mathematical induction techniques and their proofs in series expansions.
  • Investigate the implications of positive integer values of \( k \) in polynomial solutions.
USEFUL FOR

Students and educators in mathematics, particularly those studying differential equations, series solutions, and polynomial functions. This discussion is beneficial for anyone seeking to deepen their understanding of Legendre's equation and its applications in mathematical physics.

KateyLou
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Homework Statement



Obtain the recurrene relation between the coefficient ar in the series solution

y= (between r=0 and \infty) \Sigma arxr

to (1-x2)y''-2xy'+k(k+1)y=0
Deduce that if k is a positive integer, then ak+2=0, so that the equation possesses a solution which is a polynomial of degree k.

Homework Equations



(there is more to this question...but i think ill try getting through this bit first!)


The Attempt at a Solution



I have managed to get the correct recurrance relation

(n+2)(n+1)an+2-an(n(n+1)-k(k+1))=0

But i have no idea what to do now (the show if k is a positive integer) etc :-(
 
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So
a_{n+2}= a_n\frac{n(n+1)- k(k+1)}{(n+1)(n+2)}
Assume that a0 and a1[/sup] are given. What is a2, a3, a4 in terms of a0 and a1. Can you guess a form for the general an form? Can you then prove it by, say, induction?
 
i am not too sure what induction is...(sorry!) guessing a form for an - do you is this not given by the recurrance relation?
 

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