∫AB is the diameter,

∴∠ADB=90，

In the right angle △ABD, BD = ab2-ad2 = 36-25 =11,

∴, ∠ E = ∠ ADB = 90, ∠EAD=∠DAB in right-angle △ABD and right-angle △ADE.

∴△ABD∽△ADE，

∴DE BD =AD AB, that is, DE 1 1 =5 6.

∴DE=5 1 1 6，

In the right angle △ADE, AE = Ad2-De2 = 25-(5116) 2 = 256,

∫DE is the tangent of the circle,

∴DE2=CE？ AE，

∴CE=DE2 AE = 1 1 6，

∴ac=ae-ce=25 6- 1 1 6 = 7 3。

∵BC∨DE

∴△ACF∽△AED，

∴AC AE =AF AD，

∴AF=AC？ AD AE =7 3 ×5 25 6 = 14 5。