It is known that, as shown in the figure, in △ ABC, ∠ BAC = 90 ° ad ⊥ BC is at point D, be bisects ∠ ABC, intersects ad at point m, an bisects ∠ DAC, intersects BC at point n

It is known that, as shown in the figure, in △ ABC, ∠ BAC = 90 ° ad ⊥ BC is at point D, be bisects ∠ ABC, intersects ad at point m, an bisects ∠ DAC, intersects BC at point n

It is proved that: ∵ ad ⊥ BC, ∵ BDA = 90 °, ∵ BAC = 90 °, ∵ ABC + ⊥ C = 90 °, ∵ ABC + ⊥ bad = 90 °, ∵ bad = ∵ C, ∵ an bisecting ∵ DAC, ∵ can = ∵ Dan, ∵ ban = ∵ bad + ⊥ Dan, ∵ BNA = ∵ C + ≁ can, ∵ ban = ≁ BNA, ∵ be bisecting ≁ ABC, ≁ be ⊥ an