P. 534, Equation 11.52

The equation should be:

$u(x,y,t) = \sum_{n=1}^\infty \sum_{m=1}^\infty \sin \left( \frac{n \pi x}{L_x} \right) \sin \left( \frac{m \pi y}{L_y } \right) \left( a_{n,m} \sin \left( \omega_{n,m} t \right) + b_{n,m} \cos \left( \omega_{n,m} t \right) \right)$

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