$\cos \theta=\frac{a \cos \varphi-b}{a-b \cos \varphi}$

$\frac{\mathrm{a}+\mathrm{b} \sin \varphi}{\mathrm{b}-\mathbf{a} \sin \varphi}$

$\sqrt{\frac{a+b \cos \varphi}{a-b \sin \varphi}}$

$\sqrt{\frac{a+b}{a-b}}$

$\frac{\sqrt{a}+b}{b}$

$\frac{(a+b)^{2}}{a-b}$