2. By the secant rules,
BC² = DC*(DC +diameter)
Substituting the given information, you have
8² = 4*(4 +2*radius)
64 = 16 +8*radius
48/8 = radius = 6
radius = AB = 6
3. By the Pythagorean theorem,
AC² = BC² +AB²
Substituting the given information, you have
12² = 9² +AB²
144 -81 = AB² = 63
AB = √63 = 3√7
radius = AB = 3√7
