Start from Eqs. $33-11$ and $33-17$ and show that $E(x, t)$ and $B(x, t),$ the electric and magnetic field components of a plane traveling electromagnetic wave, must satisfy the "wave equations"
$$\frac{\partial^{2} E}{\partial r^{2}}=c^{2} frac{\partial^{2} E}{\partial x^{2}} \text { and } \frac{\partial^{2} B}{\partial r^{2}}=c^{2} \frac{\partial^{2} B}{\partial x^{2}}$$