Question

Q9. In a triangle ABC, write cos B+C/2 in terms of angle A.​

Answer 1

Answer:

WeknowthatA+B+C=180o[allangleofanytriangleis180∘]⇒B+C=180o−A⇒cos(2B+C)2=2180o−Acos(2180o−2A)=cos(90o−2A)=sin2AHence,2cos(B+C)=sin2A.