Geometry Problem 1241:
Quadrilateral, Four Exterior Angle Bisectors, Cyclic
Quadrilateral, Circle. Mobile
Apps. Level:
College, High School.

In a quadrilateral ABCD, the
bisectors of the exterior angles A, B, C, and D intersect at A_{1},
B_{1}, C_{1}, and D_{1}, as shown in the figure below. Prove that
quadrilateral A_{1}B_{1}C_{1}D_{1} is cyclic.

Art of Geometry Problem 1241 using Mobile Apps. Circle Patterns.

Geometric art is a form of art based on the use and application of geometric figures. A geometric figure is any set or combination of points, lines, surfaces and solids.
A mobile app or mobile application software is a computer program designed to run on smartphones and tablet computers.