$\sin(180° - \theta)$ equals:
A$-\cos\theta$
B$-\sin\theta$
C$\sin\theta$
D$\cos\theta$
Answer & Solution
Correct answer: C. $\sin\theta$
Supplementary-angle identity: $\sin(180° - \theta) = \sin\theta$.
Reason: sine is positive in the second quadrant (where $180° - \theta$ lies for $0° < \theta < 180°$), and the reference angle is $\theta$.
Companion identities:
- $\cos(180° - \theta) = -\cos\theta$
- $\tan(180° - \theta) = -\tan\theta$
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