Points $A$, $B$, and $C$ are on a circle such that $AB = 8$, $BC = 15$, and $AC = 12$. Find the radius of the circle.
The radius will be the circumradius of the triangle ABC
semi-perimeter = [ 8 + 12 + 15 ] / 2 = 17.5
Area = sqrt [17.5 (9.5) (5.5) (2.5) ]
Radius = product of the sides / 4 * area =
[8 * 12 * 15 ] / [ 4 * sqrt [17.5 (9.5) (5.5) (2.5) ] ] ≈ 7.53
+1367 
