Series solutions near a singular point, 2nd order linear

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SUMMARY

This discussion focuses on solving the 2nd order linear differential equation (lnx)y" + 0.5y' + y = 0 near the regular singular point x = 1. The indicial equation r(r-0.5) = 0 yields roots r1 = 0.5 and r2 = 0. The goal is to find the first three nonzero terms in the series solution y1 = Ʃa_n * (x-1)^(r+n) from n = 0 to infinity, specifically for the larger root. The challenge arises from the presence of the ln(x) term, complicating the extraction of a recurrence relation for the coefficients a_n.

PREREQUISITES
  • Understanding of 2nd order linear differential equations
  • Familiarity with series solutions and power series expansions
  • Knowledge of recurrence relations in the context of differential equations
  • Basic calculus, including differentiation and manipulation of logarithmic functions
NEXT STEPS
  • Learn how to replace ln(x) with a power series about x = 1
  • Study methods for solving differential equations with singular points
  • Explore recurrence relations and their applications in series solutions
  • Investigate advanced techniques for handling logarithmic terms in differential equations
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Mathematics students, particularly those studying differential equations, educators teaching advanced calculus, and researchers working on series solutions near singular points.

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So, I'm trying to solve 2nd order linear differential equations (series solutions near a singular point).

(lnx)y" + 0.5y' + y = 0 around the regular singular point x = 1

I got the indicial equation,

r(r-0.5) = 0,

which leads to the roots...

r1 = 0.5, r2 = 0

The problem only asks us to find the first three nonzero terms in the series y1 = Ʃa_n * (x-1)^r+n from n = 0 to infinity. And we only need to find one solution, corresponding to the larger root.

So I took the first and second derivatives of the y1 they gave and plugged it into the differential equation. Now at this point I usually factor out all the x terms. And since the left side has to equal zero for all x, I can divide by that x term to get a recurrence relation (that involves a_n terms). From the relation I can figure out what a_n is. However, in this case, I can't factor out all the x terms because there's a lnx.

Anyone know how to get rid of the lnx?

Thanks!

EDIT: MOVED TO HOMEWORK AND CLASSWORK SECTION
 
Last edited:
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Replace ln(x) with a power series about x= 1.
 
HallsofIvy said:
Replace ln(x) with a power series about x= 1.

Thank you.
 

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