In a triangle

MATHEMATICS · Subjective · A Level · Mathematics · Trigonometry · Trigonometry

Problem

In a triangle ABCABC, show that acos⁡A+bcos⁡B+ccos⁡Ca+b+c=rR\frac{a\cos A+b\cos B+c\cos C}{a+b+c}=\frac{r}{R}.

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