For questions about Legendre polynomials, which are solutions to a particular differential equation that frequently arises in physics.
The Legendre polynomials $P_n$ are defined to be solutions of Legendre's differential equation
$$\frac{d}{dx} \left[(1 - x^2) \frac{d}{dx} P_n(x)\right] + n(n + 1) P_n(x) = 0$$
Alternatively, by Rodrigues' formula,
$$P_n(x) = \frac{1}{2^n n!} \frac{d^n}{dx^n} \left[(x^2 - 1)^n\right]$$
The Legendre polynomials occur frequently in physics, and in particular in solving Laplace's equation in spherical coordinates.
