Paper 4, Section II, A

Asymptotic Methods | Part II, 2021

(a) Classify the nature of the point at ∞\infty for the ordinary differential equation

y′′+2xy′+(1x−1x2)y=0.y^{\prime \prime}+\frac{2}{x} y^{\prime}+\left(\frac{1}{x}-\frac{1}{x^{2}}\right) y=0 .

(b) Find a transformation from (∗)(*) to an equation of the form

u′′+q(x)u=0u^{\prime \prime}+q(x) u=0

and determine q(x)q(x).

(c) Given u(x)u(x) satisfies ( †\dagger, use the Liouville-Green method to find the first three terms in an asymptotic approximation as x→∞x \rightarrow \infty for u(x)u(x), verifying the consistency of any approximations made.

(d) Hence obtain corresponding asymptotic approximations as x→∞x \rightarrow \infty of two linearly independent solutions y(x)y(x) of (∗)(*).

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