Dividing a Triangle by Lines Parallel to Two Sides

Requires a Wolfram Notebook System
Interact on desktop, mobile and cloud with the free Wolfram Player or other Wolfram Language products.
Let ABC be a triangle and E a point on AC. Let D be on AB such that DE is parallel to BC and F be on BC such that EF is parallel to AB. Let ,
, and
be the areas of ADE, EFC, and DEFB, respectively. Then
.
Contributed by: Jay Warendorff (March 2011)
Open content licensed under CC BY-NC-SA
Snapshots
Details
See problem 1.33 in V. Prasolov, Problems in Plane and Solid Geometry, Vol. 1, Plane Geometry [PDF], (D. Leites, ed. and trans.).
Permanent Citation
"Dividing a Triangle by Lines Parallel to Two Sides"
http://demonstrations.wolfram.com/DividingATriangleByLinesParallelToTwoSides/
Wolfram Demonstrations Project
Published: March 7 2011