Cosine of Three Right Angles less Angle

Theorem

 * $\cos \left({\dfrac {3 \pi} 2 - \theta}\right) = -\sin \theta$

where $\cos$ and $\sin$ are cosine and sine respectively.

Also see

 * Sine of Three Right Angles less Angle
 * Tangent of Three Right Angles less Angle
 * Cotangent of Three Right Angles less Angle
 * Secant of Three Right Angles less Angle
 * Cosecant of Three Right Angles less Angle