Question: ab is chord of a circle with centre o?
Answer: If AB is a chord of a circle with centre ′O′AOC is a diameter and AT is the tangent is the tangent at A as shown in Figure. Prove that ∠BAT=∠ACB. Let ∠ACB = x and ∠BAT = y. The angle in a semi-circle is 90, so ∠CBA = 900.