# 11: Separation of Variables in Three Dimensions

- Page ID
- 8320

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We have up to now concentrated on 2D problems, but a lot of physics is three dimensional, and often we have spherical symmetry – that means symmetry for rotation over any angle. In these cases we use spherical coordinates, as indicated in ﬁgure 7.2.1.

- 11.1: Modelling the Eye
- Let me model the temperature in a simple model of the eye, where the eye is a sphere, and the eyelids are circular.

- 11.3: Fourier-Legendre Series
- Since Legendre’s equation is self-adjoint, we can show that they form an orthogonal set of functions.