$\displaystyle \displaystyle{ \cos\left\{ tan^{-1}\left(\frac{1}{R}\sqrt{\frac{L}{C}}\right) \right\}\stackrel{?}{=}\frac{1}{\sqrt{1+\frac{L}{R ^2C}}} }$

Even though I think it is ir-relevant: $\displaystyle R, L, C$ are resistance, inductance and capacitance, respectively.