Archimedes' Circles
Draw the Perpendicular Line from the intersection of the two small Semicircles in theArbelos. The two Circles 
and 
Tangent to this line, the large Semicircle,and each of the two Semicircles are then congruent and known as Archimedes' circles.
- Dupin's Indicatrix
- Dupin's Theorem
- Duplication Formula
- Duplication of the Cube
- Durand's Rule
- Durfee Polynomial
- Durfee Square
- Dvoretzky's Theorem
- Dyad
- Dyadic
- Dyck's Theorem
- Dye's Theorem
- Dymaxion
- Dynamical System
- Dynkin Diagram
- Dürer's Conchoid
- Dürer's Magic Square
- Dürer's Shell Curve
- e
- Ear
- Early Election Results
- Eban Number
- Eberhart's Conjecture
- Eccentric
- Eccentric Angle