if a b and c are the interior angles of triangle A B and C then show that cos B + C/ 2 is equal to sin A/2
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Step-by-step explanation:
As they are the angles of a triangle,
A+B+C=180
B+C =180 - A
(B+C)/2 =90-A/2 [dividing by 1/2]
Applying cosine on both sides ,
Cos([B+C]/2) = Cos(90-A/2)
Cos([B+C]/2) =Sin(A/2) [cos(90-A) =sinA]
Hence proved.
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