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`        Cos (a-b) +cos (b-c) + cos (c-a) = -3/2Prove that cos a + cos b+ cos c = sin a + sin b + sin c = 0 `
4 years ago

```							Cos (a-b) +cos (b-c) + cos (c-a) = -3/2multiply the equation by 2 then add 3 so that rhs becomes 0 (by doing this it becomes easy for us to solve)now expand the equation by using cos (a-b)=cos a cos b + sin a sin bwhen you do so it becomes(cos a + cos b + cos +c )2 + (sin a + sin b + sin c)2 = 0this is possible only when (cos a + cos b +cos c) = 0 = (sin a+ sin b+ sinc)HENCE PROOVED
```
4 years ago
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