Cosine of Supplementary Angle/Examples/Theta minus 180

Example of Cosine of Supplementary Angle

$\map \cos {\theta - 180 \degrees} = -\cos \theta$


Proof

\(\ds \map \cos {\theta - 180 \degrees}\) \(=\) \(\ds \map \cos {180 \degrees - \theta}\) Cosine Function is Even
\(\ds \) \(=\) \(\ds -\cos \theta\) Cosine of Supplementary Angle

$\blacksquare$


Sources

  • 1953: L. Harwood Clarke: A Note Book in Pure Mathematics ... (previous) ... (next): $\text V$. Trigonometry: Exercise $\text {XXXI}$: $9.$
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