In 2009, the 22 nd math problem in Wenzhou senior high school entrance examination was the second problem.

Add OE, because EF is the tangent of O radius.

So ∠ deo+∠ def = 90.

∠∠AEF+∠def = 90 ∴∠aef=∠aeo

∫△DBE∽△ABC ∴∠a=∠edb

∠∠edo =∠deo∴∠AEF =∠a

△ FAE is an isosceles triangle.