Answer
See below.
Work Step by Step
$sin^2(\frac{\theta}{2})=\frac{1-cos\theta}{2}\longrightarrow csc^2(\frac{\theta}{2})=\frac{1}{sin^2(\frac{\theta}{2})}=\frac{2}{1-cos\theta}$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.