Question

If A,B,C are the interior angles of a triangle ABC, find tan (B+C)/2

Answer 1

A +B+C =180
C+B/2=180-A/2
Take tangent on both side
tan(C+B)/2=tan(90-A/2 )
tan(B+C) =cotA/2

Answer 2

Answer ( B+C)/2=90-(A/2)