What is the radius of the circle inscribed in triangle $ABC$ if $AB = 12,$ $AC=14,$ $BC=20$? Express your answer in simplest radical form.
semi-perimeter, s , = (12 + 14 + 20) / 2 = 23
radius of incircle = sqrt [ ( 23 - 12) (23 - 14) (23 - 20) / 23 ] = sqrt [ 11 * 9 * 3 / 23 ] = sqrt (297 / 23) =
3 sqrt (33/23) = (3/23) sqrt (33 * 23) = (3/23)sqrt (759)
+1791 
