Question

Hello could someone please tell me which trigonometric identities do I need to apply in order to get this result?

Answer 1

\[\int\limits_{0}^{2\pi}\sqrt{1-\cos \Theta}d\]

the answer to simplification :
\[\int\limits_{0}^{2\pi}\sqrt{2\sin^2 \frac{ \theta}{ 2 }}d\]