Exam geometry: folding a rectangle

Overview

Fold rectangle along BE and study image C′ and equal lengths.

Explanation

Folding is reflection: the crease is the mirror; matching lengths and angles are equal.
Image C′ is the reflection of C across the crease.
Mark equals, then use Pythagoras, similarity, or equations for lengths.

How to use

Drag E on CD; watch C′ and EC = EC′, BC = BC′.

Knowledge points

• Exam prep
• Geometry
• Folding