According to the properties of the angular bisector, AE=AF.

So certificate 2AE=AB+AD.

AE+AF=AB+AD=(AE+EB)+(AF-DF)

Prove EB=DF

That is to say, the right triangle CDF is all equal to the right triangle CBE.

It is easy to know that CF=CE,

Because angle ADC+ angle B= angle ADC+ angle CDF= 180.

So angle EBC= angle FDC

So triangle CDF is equal to triangle CBE(AAS).