Question

If A, B, C are interior angles of triangles ABC sin ( B + C )/2

Answer 1

A + b +C=180 by angle sum property of triangle So we get B+C=180-A Putting it in the given equation we get Sin(180-A)/2=sin(90-A/2) Hence we get  Cos(A/2) which is required answer

Answer 2

Answer:

I hope it is helpful...............