Answer:
6.5 units
Step-by-step explanation:
In circle with center O, AB is diameter.
[tex] \therefore m\angle ACB = 90°\\[/tex]
(Angle inscribed in a semicircle)
[tex] \therefore \: in\: \triangle ABC, \:AB \: is\: hypotenuse \\[/tex]
By Pythagorean theorem:
[tex]AB = \sqrt{ {12}^{2} + {5}^{2} } \\ = \sqrt{144 + 25} \\ = \sqrt{169} \\ AB \: = 13 \\ r = \frac{13}{2} = 6.5 \: units[/tex]
