Reference for "tangent of half angle equals cosecant minus cotangent" The identity $\tan(\frac{\theta}{2})=\frac{1-\cos \theta}{\sin \theta}$ is easily seen to be equivalent to $\tan(\frac{\theta}{2})=\csc \theta - \c...--prophetes.ai

Reference for "tangent of half angle equals cosecant minus cotangent" The identity $\tan(\frac{\theta}{2})=\frac{1-\cos \theta}{\sin \theta}$ is easily seen to be equivalent to $\tan(\frac{\theta}{2})=\csc \theta - \cot \theta$. So, my question is: Are there any (online or offline) sources (other than Wikipedia) that mention the latter identity involving cosecant and cotangent? The answer may, for example, be a textbook, an online book on Google Books, or a PDF file.

It shows up in Schaum's Mathematical Handbook.pdf) as formula 5.43 (on p.16).