How to solve the problem of 20 1 1 Ningbo senior high school entrance examination mathematics 17? How to extend AD in F to BC, and ED in H to BC.

Ab = AC ∴BF=FC= 1/2BC

∵ Angle EBCD= angle bed =60, so △BEH is an equilateral triangle, so BH=BE=6, so

DH=4。 In Rt△DEH, FH= 1/2DH=2. So BF=4, ∴BC=8.