Question

if A ,B and C are interior angle of an tringle ABC. then cos (B+C/2) is equal to ​

Answer 1

Answer:

A + B + C = 180°

B + C = 180° - A

Divide both sides by 2

B+C / 2 = 180/2 - A/2

B+C /2 = 90 - A/2

Apply cos on both sides

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

cos(B+C/2) = sin(A/2)