Connect FC so that BAE=a and EAD=2a.
∫ The quadrilateral ABCD is a diamond.
∴AB=BC=CD=DA=AE (and parallel)
∴ Angle AEC= 180 degrees -2a
∵ Angle FCE= Angle FAB=a (if you don't believe it, you can prove congruence)
∴ angle EFC= 180 degrees -( 180 degrees-2a)-a = a.
∴EF=EC
∴AE-EF=BC-EC
∴AF=BE
aha
Don't thank me too much.
I am really a good man.
I'm also in Grade Two.
You work harder than me? ! ! !