Question
If A + B + C =
, then cos A + cos B – cos C =
- – 1 + 4 sin A/2 cos B/2 sin C/2
- – 1 + 4 cos A/2 sin B/2 sin C/2
- 4 cos A/2 sin B/2 sin C/2
- – 1 + 4 cos A/2 cos B/2 sin C/2
The correct answer is: – 1 + 4 cos A/2 cos B/2 sin C/2
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