In any triangle \( A B C \), prove that \[ (b+c) \cos A+(c+a) \cos B+(a+b) \cos C=a+b+c \]

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In any triangle \( A B C \), prove that
\[
(b+c) \cos A+(c+a) \cos B+(a+b) \cos C=a+b+c
\]
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