Question

如图,已知在四边形ABCD中,AB=4cm,AD=7cm,∠ABC的平分线BF交AD于点E,交CD得延长线于点F,求DF

Answer 1

∵BF平分∠ABC,

∴∠ABE=∠CBE,

又∵AB∥CD,

∴∠ABE=∠BFC,

∴∠CBE=∠BFC,

∴BC=CF,

∴DF=CF-CD=BC-AB=7-4=3．