Question

in a triangle ABC,write cos(b/2+c/2)in terms of A

Answer 1

we know that sum of all the angels of a triangle = 180
so here we have a+b+c = 180°
b+c = 180-a
now coming to the question cos((b+c)/2) = cos((180-a)/2) = cos(90-a/2) = sin(a/2)
hence the answer is sin(a/2)

Answer 2

This should be your answer.