The measure of arc CB is 2 times 48. (An inscribed angle is one-half the measure of its intercepted arc. The intercepted arc is angle CDB). Arc CB is 96, and angle COB is 96 (An arc is congruent to its central angle, vice versa).
An exterior angle is equal to one-half the difference of its two intercepted arcs. The two intercepted arcs of angle A are major arc CDB and minor arc CB. CDBC (all the way around) has to equal 360, so 360-96=264. One-half of that is 132°, the measure of ∠A.
