show that each complex exponential is also a solution of the 1-D wave equation. Now using Euler's formula you found that [tex]cos({\omega}t-kx_{1}) = \frac{e^{j({\omega}t-kx_{1})}+e^{-j({\omega}t-kx_{1})}}{2}[/tex] right? Superposition , if you didn't know, means algebraic sum. So what would be the two complex exponentials which summed give you [tex]P(t,x_{1})=cos({\omega}t-kx_{1})[/tex] ? I'm sure you