菱形ABCD中,AE=AB,
∠B=∠D,∠BAD=∠BCD,AE=AB=BC=CD=DA,∠B=∠BEA=∠D=∠DFA,∴∠BAD=∠DAF;
△AEF是正三角形,∴∠EAF=∠AFE=∠FEA=60°,
∠CEF=180°-60°-∠BEA=120°-∠BEA,
∠CFE=180°-60°-∠DFA=120°-∠BEA,[∵∠B=∠BEA=∠D=∠DFA]
∴∠CEF=∠CFE=120°-∠BEA,
∠BAD=∠BAE+60°+∠FAD=2∠BAE+60°=2(180°-∠B-∠BEA)+60°=420°-4∠B,
∠BCD=180°-∠CEF-∠CFE=180-(120°-∠BEA)-(120°-∠BEA)=-60°+2∠B,
420°-4∠B=-60°+2∠B,
6∠B=480°
∠B=80°