What is the radius of the circle inscribed in triangle $ABC$ if $AB = 12, AC=14, BC=16$? Express your answer in simplest radical form.
r = 2 * area / perimeter
semi-perimeter, S = (12 + 14 + 16) / 2 = 21
Area = sqrt [ 21 ( 21 - 16) (21 - 14) ( 21 -12) ] =
sqrt [ 21 * 5 * 7 * 9 ] = 21sqrt (15)
r = 2 * 21 sqrt (15) / 42 = sqrt (15)
+206 
