As shown in the figure, ad is the angular bisector of the outer angle of the triangle ABC. The intersection of AD and the circumscribed circle of the triangle ABC is at point D

As shown in the figure, ad is the angular bisector of the outer angle of the triangle ABC. The intersection of AD and the circumscribed circle of the triangle ABC is at point D

∠BCD+∠BAD=180
Therefore, BCD = DAE
In this paper, we discuss the relationship between ∠ CBD = ∠ CAD (in the same arc), ∠ CAD = ∠ DAE, so ∠ DAE = ∠ CBD
The result is: BCD = CBD
DB=DC