As shown in the figure, in △ ABC, the bisector of ∠ a = 90 ° and ∠ B intersects AC at D, ah and DF are perpendicular to BC, h and F are perpendicular feet

As shown in the figure, in △ ABC, the bisector of ∠ a = 90 ° and ∠ B intersects AC at D, ah and DF are perpendicular to BC, h and F are perpendicular feet

It is proved that: the bisector of ∵ B intersects at D, ≌ abd = ≌ DBF, in △ abd and △ FBD, ≌ abd = ≌ DBF, ad = DF, ≔ ah ⊥ BC, DF ⊥ BC, namely AE ∥ DF, ∥ AED = EDF = ade, ∥ AE = ad, ad = DF, ∥ AE = DF and AE ∥ DF, ∥ quadrilateral aefd is parallelogram, ∥ EF = ad and AE = ad = DF, ∥ AE = DF in parallelogram aefd, AE = ad = DF = EF, ∥ aefd is diamond