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+(1x1x2)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 xx \rightarrow \infty for u(x)u(x), verifying the consistency of any approximations made.

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