∠∠DAC =∠∠FBC (the outer angle of the inscribed quadrangle of a circle is equal to the inner diagonal)
EAD=∠BAF=∠BCF
∠DAC=∠EAD
∴∠FBC=∠BCF
∴FB=FC
2.
∵∠ FAC +∠ FBC = 180 (diagonal complementation of inscribed quadrangles of a circle)
∠FCD+∠BCF= 180
FBC=∠BCF
∴∠FAC=∠FCD
And ∵∠AFC is the male angle.
∴△FAC∽△FCD
∴FC/FD=FA/FC
Namely FC? =FD*FA
FC = FB
∴FB? =FD*FA