- #1

xavierhart

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This was the first exercise in the book and so far it has only stated the Law of Sines, so I'm assuming that I won't need anything else to show that a=b cos C + c cos B. Especially seeing at it says that in the question! Haha.

## Homework Statement

Show that, for any triangle ABC, even if B or C is an obtuse angle, a=b cos C + c cos B. Use the Law of Sines to deduce the "addition formula":

sin(B+C) = sin B cos C + sin C cos B

## Homework Equations

Law of Sines is all that has been stated so far.

## The Attempt at a Solution

Non-existent as of yet, apart from stating different sides in terms of trig functions of the angles, but getting nowhere.

I understand this question may be quite trivial in the end seeing as it is the first one in the book, but I would appreciate any points in the right direction.