Trigonometrymedium · Past Paper
Evaluate: cos 10° cos 20° - sin 10° sin 20°.
Asin 30°
Bcos 30°
Ctan 30°
Dcos 10°
✓ Correct Answer: B — cos 30°
Using cos(A+B) = cos A cos B - sin A sin B, we get cos(10+20) = cos 30°.
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