Trigonometryhard · Past Paper
If A+B+C = 180, then cos 2A + cos 2B + cos 2C = ?
A-1 - 4 cos A cos B cos C
B1 - 4 sin A sin B sin C
C4 cos A cos B cos C
D1 + 4 cos A cos B cos C
✓ Correct Answer: A — -1 - 4 cos A cos B cos C
This is a standard conditional identity for cosines of double angles in a triangle.
Share this question
More from Trigonometry
- Simplify: (cos A + sin A) / (cos A - sin A) - (cos A - sin A) / (cos A + sin A).
- If the height of a pole is increased by 10%, and the angle of elevation remains 45°, the shadow length:
- The line of sight is the line joining the observer's eye to the:
- What is the value of tan 3A - tan 2A - tan A?
- What is the value of sin 60 * cos 30 + cos 60 * sin 30?