2140 - Notes, Syllabus Section VI, lecture 38 (11/29/95)

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Series solutions to differential equations

Boas 12.1, 12.2

Caveat that this doesn't always work (e.g. if y=log(x))

Example of simple equation (y'=2yx) solved directly, and then as a series

Legendre's equation - discussion of where it comes from

(1-x^2)y'' - 2x y' +l(l+1)y=0, with l any constant (usually a postive integer)

Power series solution, calculated general solution, found particular solution when l is an integer, and which is 1 at x=1 => "The Legendre polynomials". (Mentioned Legendre function of the second kind, which are not polynomials, and which diverge at x=1)

Qualitative discussion of these polynomials, and how they are vaguely reminiscent of sin's and cos's.


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