Question

ABC are interior angles of a tiangle show that 1) sin[B+C] =COS A
2 2

Answer 1

Step-by-step explanation:

Sin (B+C)/2 = Cos(A/2) - - - - >(i)

By using the identity - CosA = Sin(90-A) we get,

Sin(90-A/2) = Cos(A/2)

Put the value of sin (B+C/2) in equation (i)

Sin(B+C/2) = Sin(90-A/2)

Sin(B+C /2) = Sin(180/2-A/2)

B+C = 180-A

B+C+A = 180

So,

B+C A

Sin (------) = Cos (-----)

2 2

Thank you...