Given that AOC is the diameter and AO na d OB are the radii, then ΔAOB is an isosceles triangle. Thus the base angles ∠A=∠B
thus
∠BAC=∠A will be found as follows:
sum of angles in a triangle is 180
thus
180-87=
=93
hence
∠A=∠B=93/2=46.5°
Answer: 46.5°