Trigonometryhard · Past Paper
In triangle ABC, cos^2 A + cos^2 B + cos^2 C = ?
A1 - 2 cos A cos B cos C
B1 + 2 cos A cos B cos C
C2 sin A sin B sin C
D1 - 2 sin A sin B sin C
✓ Correct Answer: A — 1 - 2 cos A cos B cos C
Conditional identity for sum of squares of cosines in a triangle.
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