m=1.2m,dn=1.5m
由相似三角形的比例关系可得
EF:AB=EM:BM,则EM=0.18
EF:CD=EN:ND 则EN=0.225
BD=BN+ND
=BM--MN+ND
=1.2-(0.18+0.225)+1.5
=2.295m