2

Part of 2021 Austrian MO Regional Competition

Problems(1)

BC is tangent to circumcircle of BDE, isosceles ABC

Source: 2021 Austrian Regional Competition For Advanced Students p2

ABC

be an isosceles triangle with

AC = BC

and circumcircle

k

D

lies on the shorter arc of

k

BC

and is different from

B

C

E

denote the intersection of

CD

AB

. Prove that the line through

B

C

is a tangent of the circumcircle of the triangle

BDE

.
(Karl Czakler)

geometrytangentisoscelesAZE CMO TSTAZE EGMO TST