∵平行四边形ABCD
∴∠ADO=∠CBO,DO=BO
∵∠DON=∠BOM
∴△DON≌△BOM (ASA)
∴DN=BM,ON=OM
∴四边形ABMN的周长=AB+BM+MN+AN
=AB+AN+DN+OM+ON
=AB+AD+2OM
=6+4+4
=14(cm)
∵平行四边形ABCD
∴∠ADO=∠CBO,DO=BO
∵∠DON=∠BOM
∴△DON≌△BOM (ASA)
∴DN=BM,ON=OM
∴四边形ABMN的周长=AB+BM+MN+AN
=AB+AN+DN+OM+ON
=AB+AD+2OM
=6+4+4
=14(cm)