- #1

harimakenji

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## Homework Statement

show that

(a cos A - b cos B) / (b cos A - a cos B)= cos C

if ABC is triangle

## Homework Equations

trigonometry identity

## The Attempt at a Solution

A + B + C = 180

^{o}

A = 180

^{o}- (B+C)

cos A = - cos (B+C)

substitute cos A to the LHS: (- a cos (B+C) - b cos B) / (b cos A - a cos B) = (-a cos B cos C + a sin B sin C - b cos B) / (b cos A - a cos B)

How to continue? Thank you very much