Cosecant of Complement equals Secant

Theorem

 * $\csc \left({\dfrac \pi 2 - \theta}\right) = \sec \theta$ for $\theta \ne \left({2 n + 1}\right) \dfrac \pi 2$

where $\csc$ and $\sec$ are cosecant and secant respectively.

That is, the secant of an angle is the cosecant of its complement.

This relation is defined wherever $\sin \theta \ne 0$.

Proof
The above is valid only where $\cos \theta \ne 0$, as otherwise $\dfrac 1 {\cos \theta}$ is undefined.

From Cosine of Half-Integer Multiple of Pi it follows that this happens when $\theta \ne \left({2 n + 1}\right) \dfrac \pi 2$.