Reciprocal of One Plus Cosine

Theorem

 * $\dfrac 1 {1 + \cos x} = \dfrac 1 2 \sec^2 \left({\dfrac x 2}\right)$

Also see

 * Reciprocal of One Minus Cosine


 * Reciprocal of One Plus Sine
 * Reciprocal of One Minus Sine