Question

在梯形ABCD中AD平行于BC,AB=DC∠D=120°AC平分∠BCD若AE平行DC,梯形ABCD周长20cm,求BC

Answer 1

AD平行于BC,AC平分∠BCD => AD=DC;

AD平行于BC,AE平行DC =>ADCE为平行四边形 =>AD=CE,AE=DC;

AD平行于BC,∠D=120°,AB=DC =>∠B=∠BCD=60°;

AB=DC ,AE=DC ,∠B=60°=>AB=BE =>BC=BE+CE=2CD;

AD+DC+BC+AB=5CD=20cm,

CD=4cm,

BC=8cm