Question

in a triangle write cos b+c/2 in terms in angle a

Answer 1

The sum of angles in a triangle is 180 degrees 

which means ..... a + b + c = 180

b+c = 180- a

cos ( 180 - a /2)      ............   ( as   b+ c = 180 - a)

we get 

cos ( 90 - a/2 )
which is equal to

sin ( a/2)