Question

BD平分∠ABC，DE∥AB,EF∥BD,请问EF平分∠DEC吗？为什么？

Answer 1

DE∥AB,所以∠DEC = ∠ABC

EF∥BD,所以∠DEF = ∠BDE,再次根据DE∥AB,有∠BDE = ∠ABD

所以∠DEF = ∠ABD = 1/2 ∠ABC =1/2∠DEC

所以EF平分∠DEC得证