Hi, I have a maths exam tommorrow (!) and I'm stuck on something: Its about solving LaPlace's equation in plane polar coordinates. There is a circular plate witha temp dist that satisfies (1/r)(d/dr(r.df/dr)) + 1/r2 . d2/dp2 = 0 (p is phi) so I used a separable eq of the form f=RP and solved it to get R = Crm+Dr-m when m doesn't equal 0 and R(r) = A + B ln(r) when m=0 The question is: What boundary condition does R(r) satisfy at r = 0? Use this to show that the general solution to this problem is f= A0 + SUM OF(rm)( Am cos(mp) + Bm sin(mp)) the explanation is because you can't have negative powers of m when R(r) is finite at the centre. Why can't you have negative powers of m? Negative powers will give fractions but they will still be finite, so why isn't it f= A0 + SUM OF(Cmrm+Dmr-m)( Am cos(mp) + Bm sin(mp)) Thanks if you can help before tommorrow!