Please help is solving the non homogeneous heat problem.

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Homework Statement


Find solution of a nonhomogeneous heat problem:

\frac{\partial U}{\partial t} = c^2( \frac{\partial^2 U}{\partial r^2} + \frac{1}{r}\frac{\partial U}{\partial r} + \frac{1}{r^2}\frac{\partial^2 U}{\partial \theta^2} + g(r,\theta,t)

With boundary condition: U(a,\theta, t) = 0

Initial condition: U(r,\theta,0) = f(r,\theta)



2. The attempt at a solution 1

The associate homogeneous equation is:

U(r,\theta,t)=R\Theta T \;\;\;\;\Rightarrow\;\;\;\; R\Theta T' + c^2(R''\Theta T + \frac{1}{r}R'\Theta T + \frac{1}{r^2}R\Theta'' T)= g(r,\theta,t)

Where U_c(r,\theta,t) = \sum_{m=0}^{\infty}\sum_{n=1}^{\infty}J_m(\lambda_{mn}r)[A_{mn}cos(m\theta) + B_{mn} sin(m\theta)]e^{-c^2\lambda^2_{mn}t}

I don't know how to solve for particular solution.
 
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Anyone please? I just want some guidance how to approach this problem.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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