Question

if A,B, and C are interior angles of a triangle of ABC then show that,
$\sin(b + c \div 2 =) \cos(a \div 2)$
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Answer 1

A+B+C=180 degrees
So B+C=180-A
(B+c)/2 =180/2-A/2
Sin (B+C)/2 = sin (90-A/2 )
= CosA/2