Fuente TeX:

\frac{cos(\theta)+1}{1- cos(\theta)} = \frac{cos^2(\frac{\theta}{2}) - sin^2(\frac{\theta}{2}) + cos^2(\frac{\theta}{2}) + sin^2(\frac{\theta}{2})}{cos^2(\frac{\theta}{2}) + sin^2(\frac{\theta}{2}) - ( cos^2(\frac{\theta}{2}) - sin^2(\frac{\theta}{2}))} =\frac{cos^2(\frac{\theta}{2})}{sin^2(\frac{\theta}{2})} = \frac{1}{tan^2(\frac{\theta}{2})}