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).