$x = \frac{{1 – \sin \phi }}{{\cos \phi }}\,\, = \,\,\frac{{1 – \cos (\pi /2 – \phi )}}{{\sin (\pi /2 – \phi )}}$ $= tan(\pi /4-\phi /2)$

$y = \frac{{1 + \cos \phi }}{{\sin \phi }}\,\, = \,\,\frac{{2\,{{\cos }^2}\phi /2}}{{2\sin (\phi /2)\,\cos (\phi /2)}}$ $= cot\, \phi /2$

$x = \frac{{1 – \tan \phi /2}}{{1 + \tan \phi /2}}$ $=$$\frac{{\cot \phi /2\, – \,1}}{{\cot \phi /2\, + 1}}\,\, = \,\,\frac{{y – 1}}{{y + 1}}$

Applying $C/D$ $\frac{{x + 1}}{{x – 1}}\,\, = \,\,\frac{{y – 1 + y + 1}}{{y – 1 – y – 1}}\,\, = \,\,y$

Also ,$y =$$\frac{{x + 1}}{{1 – x}}\,\, \Rightarrow $ $y – xy – x-1 = 0$