
theorem Thm26:
  for A,B,C be Point of TOP-REAL 2, r being positive Real st
  angle(A,B,C) is non zero
  holds sin (r * angle (C,B,A))=
  sin (r * 2 * PI) * cos (r * angle(A,B,C)) - cos (r * 2 * PI) *
  sin (r * angle(A,B,C))
  proof
    let A,B,C be Point of TOP-REAL 2,r being positive Real;
    assume angle(A,B,C) is non zero; then
    angle(C,B,A)= 2 * PI - angle(A,B,C) by EUCLID_3:37;
    then r * angle(C,B,A)= r * 2 * PI - r * angle(A,B,C);
    hence thesis by SIN_COS:82;
  end;
