Sine and Cosine of Supplementary Angles

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Theorem

Sine of Supplementary Angle

$\sin \paren {\pi - \theta} = \sin \theta$

where $\sin$ denotes sine.


That is, the sine of an angle equals its supplement.


Cosine of Supplementary Angle

$\map \cos {\pi - \theta} = -\cos \theta$

where $\cos$ denotes cosine.


That is, the cosine of an angle is the negative of its supplement.