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Prove that: cos 80^0+cos 40^0-cos 20^0=0...

Prove that: `cos 80^0+cos 40^0-cos 20^0=0`

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To prove that \( \cos 80^\circ + \cos 40^\circ - \cos 20^\circ = 0 \), we can use the cosine addition formula. ### Step-by-Step Solution: 1. **Identify the expression**: We start with the expression: \[ \cos 80^\circ + \cos 40^\circ - \cos 20^\circ \] ...
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