Given AC=3, BD=5, AB=17 Need to find internal tangent CD Extend radius AC by 5 units to E, where CE is 5 units long. then Draw BE, so that CDBE is a rectangle. Now triangle ABE is a right triangle, with shorter leg AE = 3+5 = 8, and hypotenuse AB which is given to be 17. So by the Pythagorean theorem, And since CDBE is a rectangle, CD = EB = 15 So the internal tangent, CD, is 15 units. Edwin