Orthologic
Two Triangles 
and 
are orthologic if the perpendiculars from theVertices 
, 
, 
on the sides 
, 
, and 
pass through one point.This point is known as the orthology center of Triangle 1 with respect to Triangle 2.
- Euler's Phi Function
- Euler's Polygon Division Problem
- Euler's Quadratic Residue Theorem
- Euler Square
- Euler's Rotation Theorem
- Euler's Rule
- Euler's Series Transformation
- Euler's Spiral
- Euler's Sum of Powers Conjecture
- Euler's Theorem
- Euler's Totient Rule
- Euler's Transform
- Euler's Triangle
- Euler Sum
- Euler Totient Function
- Euler Transformation
- Euler Triangle Formula
- Euler Walk
- Euler Zigzag Number
- Eutactic Star
- Evans Point
- Eve
- Even Function
- Even Number
- Eventually Periodic