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angle chasing in ABCD, 80^o, 20^o, 20^o (2021 Novosibirsk Oral Geo Oly 7.2)

Source:

April 27, 2021

geometryangles

Problem Statement

The extensions of two opposite sides of the convex quadrilateral intersect and form an angle of

20^o

, the extensions of the other two sides also intersect and form an angle of

20^o

. It is known that exactly one angle of the quadrilateral is

80^o

. Find all of its other angles.