Question

in triangle ABC ,write cos(B+C)/2 in terms of angle A.

Answer 1

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)

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)tep-by-step explanation: