In a A B C , if tan(A/2),tan(B/2),tan(C...

In a ` A B C ,` if `tan(A/2),tan(B/2),tan(C/2)` are in AP, then show that `cosA ,cosB ,cosC` are in `AdotPdot`

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The correct Answer is:

`cos B -cos A =cos C-cos B.`

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