The dynamic figure above shows a triangle
ABC, D, E, and F are the tangency points with the incircle I. DG and EH
are parallel to AB so that G is on EF and H is on FD extended. If DE and
GH meet at K, prove that C,K,F are collinear.
Dynamic Geometry of Problem 895
The interactive demonstration above was created with GeoGebra.
To stop/play the animation: tap the icon in the
lower left corner.
To reset the interactive figure to its initial state: tap the icon in the
upper right corner.
To manipulate the interactive figure: tap and drag points or lines.
GeoGebra
GeoGebra is free and multiplatform dynamic mathematics software for all levels of education that joins geometry, algebra, tables, graphing, statistics and calculus
application, intended for teachers and students. Many parts of GeoGebra have
been ported to HTML5. It has received several educational software awards in Europe and the USA.
