Plane wave equations referenced to the Z axis

$$\begin{eqnarray} W(\theta) = \frac {W_{z}^3 C^{6} + W_{z}^2 (2W_{x} + W_{xnmo})... ..._{x}^2 C^{2}S^{4} + W_{x}^3 S^{6}} {(W_{z} C^{2} + W_{x} S^{2})^2}\end{eqnarray}$$ (7)