hey everyone,
i have to show that in a triangle, there is : (A, B, C are the angles of that triangle)
\sin \left( 1/2\,B \right) \cos \left( 1/2\,C \right) +\sin \left( 1/2
\,C \right) \cos \left( 1/2\,B \right) =\cos \left( 1/2\,A \right)
for this one, here is what i got to...