Solving a partial differential equation

Haorong Wu
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Homework Statement
##(\partial_t^2-\partial_z^2) h(t,z)=A \cos (k(t-z))##
Relevant Equations
None
If the right-hand side is zero, then it will be a wave equation, which can be easily solved. The right-hand side term looks like a forced-oscillation term. However, I only know how to solve a forced oscillation system in one dimension. I do not know how to tackle it in two dimensions.

I have tried to generalize it into two dimensions by solving it pretending ##h## depends only on ##t## and ##z## separately, but I have no clues on how to carry on.

I have tried it in Mathematica. It gives no results.

Thanks ahead.
 
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Try changing variables to ##\xi = z-t## and ##\eta = z+t##.
 
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This is special case of the inhomogeneous wave equation or wave equation with source term. The so called source term is the right hand side. If the right hand side is zero, we have the homogeneous wave equation or simply wave equation.
 
Thanks, @Orodruin and @Delta2.

By changing variables with ##t-z=\alpha## and ##t+z=\beta##, I found that the equation becomes ## \partial_\alpha \partial_\beta=\frac A 4 \cos (k\alpha)##, which can be easily solved.
 
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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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