### Proposition

The figure below shows
a circle with diameter AB. Line CD is a tangent at D (C on AB extended).
Line EA is perpendicular to AB (E on BD extended) and BF is perpendicular
to AB (F on AD extended). Prove that the points E, F, and C are collinear.

## Sketch of Problem 1397 using iPad Apps

## Circular Patterns of Problem 1397 using iPad Apps

## Geometric Art
using Mobile Apps

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.