- #1

JesseC

- 251

- 2

"

For

*r*< 1 we can make a series expansion of [itex]f(r,u)[/itex] in terms of powers of r where:

[tex] f(r,u) = \frac{1}{\sqrt{1+r^2-2ru}} = \sum^{\infty}_{n=0}r^nP_n(u) [/tex]

"

Where [itex]P_n(u)[/itex] is a function of

*u*(and is actually the Legendre polynomials). This was stated without real explanation. I don't understand how you can just 'see' this series expansion from the form of [itex]f(r,u)[/itex]. I'm probably just missing some prerequisite maths knowledge so if anyone could point me in the right direction, I'd appreciate it.