Interactive resource
Similarity models (A / figure-8)
Geometry. Proportional segments in the A-frame and figure-8 configurations. Free interactive GeoGebra resource — adjust parameters in the browser.
Overview
Proportional segments in the A-frame and figure-8 configurations.
Explanation
A-frame: a line parallel to one side cuts the other two proportionally (or yields similar triangles).
Figure-8: intersecting lines with a parallel produce opposite similar triangles and proportional sides.
Key: spot parallels first, then write similarity or proportions.
How to use
Switch models; drag DE or the four endpoints and watch ratios stay equal.