As shown in the figure, in the triangle ABC, ad bisects ∠ BAC, BC intersects D, e and F are the points on AB and AC respectively. If the angle AED + ∠ AFD = 180 °, then de = DF

As shown in the figure, in the triangle ABC, ad bisects ∠ BAC, BC intersects D, e and F are the points on AB and AC respectively. If the angle AED + ∠ AFD = 180 °, then de = DF

∵ - ACD + AFD = 180 °, a, e, D and F are in the same circle, and ∵ DAE = DAF, ∵ de = DF