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Unit Circle, important angles

December 5, 2016 Mouctar Trigonometry 0

Angles greater than 180 degrees

Looking at the following figure, we can see that $\triangle AEB' \cong \triangle ADC_1$ by the AAS postulate.

$\angle EAB' =\angle DAC'_1$

The actual angle is $\pi+\beta$

Using CPCTC:

$\sin (\pi+\alpha)= -\sin \alpha$

$\cos (\pi+\alpha)= -\cos \alpha$

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