Question

In a triangle ABC, cos
(B+ C)÷2in terms of angle A.​

Answer 1

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➠A+B+C = 180 (ASP of trianlge)

➠ B + C  = 180 - A

➠ cos (B + C) / 2 = cos (180 - A) / 2

➠ cos (180/2 - A/2)

➠cos (90 - A/2)

➠sin (A/2)

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

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Answer 2

Answer:

➠A+B+C = 180 (ASP of trianlge)

➠ B + C = 180 - A

➠ cos (B + C) / 2 = cos (180 - A) / 2

➠ cos (180/2 - A/2)

➠cos (90 - A/2)

➠sin (A/2)

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