louisatanhuiying
Banned
- Joined
- Sep 24, 2012
- Messages
- 6
In Triangle ABC, prove that cosA + cosB + cosC = 1 + 4sin(A/2)sin(B/2)sin(C/2).
I've tried the 3 basic trigo formulas for triangles but they always end up in some dead end, but I'm guessing that only these 3 are needed because this is a 'basic' question so I don't think complex formulas are needed. Thank you!
I've tried the 3 basic trigo formulas for triangles but they always end up in some dead end, but I'm guessing that only these 3 are needed because this is a 'basic' question so I don't think complex formulas are needed. Thank you!