1. The problem statement, all variables and given/known data How can I prove this theorem in the triangle ABC? sin(A)/a=sin(B)/b=sin(C)/c 2. Relevant equations A*B and ... 3. The attempt at a solution I have drawn a triangle and tried to prove it, but i couldn't. (I don't know how to send a picture to my post!) I know how to prove the cosine theorem but i can't prove the sine theorem.