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Prove that (cos C + cos A)/(c + a) + (co...

Prove that `(cos C + cos A)/(c + a) + (cos B)/(b) = (1)/(b)`

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`(cos C + cos A)/(c + a) + (cos B)/(b)`
`= ((b cos C + c cos B) + (b cos A + a cos B))/(b(c + a))`
`= (a + c)/(b(c + a)) = (1)/(b)`
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