Question

In a triangle ABC,write cos(B+C/2)in the therms of A.

Answer 1

Cos {(B+C)/2}

In the triangle all angles will add upto 180° so, <B+<C+<A = 180°
<B+<C= 180°-<A

Cos{ ( B+C)/2 } = Cos {(180-<A)/2) = Cos (90-<A/2)

HOPE this helps you :)