延长CD交AB于点M,延长DC交EF于NABC=30,BC垂直于CD, 即ABC=30,BCD=BCM=90, 推出CMB=60因为 AB//EF,所以CNE=CMB=60,(内错角)又因 DEF=45,则 CDE=NDE=180-DNE-DEF=180-60-45=75所以,CDE=75.
