​ If A, B and C are interior angles of a triangle ABC, then show that sin((B + C)/2) = cos (A/2)

Question

If A, B and C are interior angles of a triangle ABC, then show that sin(\(\frac{B + C}{2}\)) = cos\(\frac{A}{2}\)

Answer 1

A + B + C = 180° 

B + C = 180 – A