(a) 8 cm
Since the lengths of tangents drawn from a point to a circle are equal, PA = PB.
Therefore, PAB = PBA = x° (say)
Then, x° + x° + 60° = 180°
⇒2x° = 120°
⇒ x° = 60°
∴ Each angle of ΔPAB is 60°; therefore, it is an equilateral triangle.
∴ AB = PA = PB = 8 cm