The equation should be
u ( x , y ) = ∑ n = 1 ∞ c n sin n π x L x ( e n π y / L x − e − n π y / L x ) {\displaystyle u(x,y)=\sum _{n=1}^{\infty }c_{n}\sin {\frac {n\pi x}{L_{x}}}\left(e^{n\pi y/L_{x}}-e^{-n\pi y/L_{x}}\right)}
Return to errata.