Formulaes for finding the solution for negative angle trigonometric equations:
\begin{align} \sin (-\alpha) &= -\sin \alpha \\ \\ \cos (-\alpha) &= \cos \alpha \\ \\ \tan (-\alpha) &= -\tan \alpha \\ \\ \cot (-\alpha) &= -\cot \alpha \\ \end{align}
See also:
Negative Angle FAQ
What are negative angle trigonometric formulas?
They show how sine, cosine, tangent, and cotangent behave when the angle sign is negative.
Which functions change sign for negative angles?
Sine, tangent, and cotangent change sign, while cosine stays the same.
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