Answer:
∠ BAC = 28.5°
Step-by-step explanation:
∠ AOB = 180° - 57° = 123° ( straight angle )
OA and OB are congruent ( radii of the circle ) , then Δ AOB is isosceles with base angles congruent, that is
∠ BAC = ∠ ABO , then
∠ BAC = [tex]\frac{180-123}{2}[/tex] = [tex]\frac{57}{2}[/tex] = 28.5°
