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For any triangle ABC, prove that(cosA)/a...

For any triangle ABC, prove that`(cosA)/a+(cosB)/b+(cosC)/c=(a^2+b^2+c^2)/(2a b c)`

Text Solution

Verified by Experts

By cosine law of triangles we have:
`c^2 = a^2 + b^2 − 2ab cos(C)`
`cos(C) = (c^2 - a^2 - b^2) / (-2ab) `
`=>cos(C) = (a^2 + b^2 - c^2)/2ab` ...
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