Interesting Triangles Phenomenon

Creation of this resource was inspired by a problem that appears in the November 2021 [i]Mathematics Teachers' Journal [/i]published by the [url=https://twitter.com/AMTNYS]Association of Mathematics Teachers of New York State (@AMTNYS)[/url]. [br][br]This problem was proposed by James M. Parks from SUNY (Potsdam, NY).
Given angle ADB and DBC are supplementary and AB = DC, how can we prove what is shown towards the end of this animation?
Quick (silent) demo
– Tim Brzezinski

Information: Interesting Triangles Phenomenon