Heat conduction problem in a ring of radius a

[rx24race]

Homework Statement

We previously solved the heat conduction problem in a ring of radius a, and the solution is

c into the sum, perform the sum first (which is just a geometric series), and obtain the general solution, which should only involve one integral in ϑ

Homework Equations

The Attempt at a Solution

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[Ellazhu223]

where is this geometric series come from Never seen it before