Question

if a b and c are interior angle of triangle ABC then show that sin b + c upon 2 is equal to cos A upon 2

Answer 1

A+B+C=180. (A.s.p)
B+C=180-A
B+C\2=90 -A\2
sin(b+c\2)=sin(90-a\2)
sin(b+c\2)=cosa\2. [sin(90- Q)=cos
]