What is the value of cos (90° - B) sin (C - A) + sin (90° + A) cos(B + C) - sin (90° - C) cos (A+B)?

sin (A+B+C) sin (A + B - C) 0 1

0

Put A = B = C = 45° cos (90° - B) sin (C - A) + sin (90° + A) cos (B + C) - sin (90° - C) cos ( A + B) = 0 because sin (C - A) = 0, cos (B + C) = 0, cos (A + B) = 0