菱形的边长相等,对角线互相垂直平分,对边平行∵∠BAD=120º∴∠ABC=60º∵AB=BC∴⊿ABC是等边三角形∴AC=边长=4cm,AO=½AC=2cmBO²=AB²-AO²=16-4=12(cm²)BO =2√3cmBD =2BO=4√3 cm...