Adams' Circle Theorem

Monge & d'Alembert Three Circles Theorem II with Dynamic Geometry

Miquel's Pentagram with Dynamic Geometry.

Nine-Point Center, Nine-Point Circle, Euler Line.

22 Interactive steps

Proposed Problem 39.
Triangle, Incircle, Bisector, Cyclic Quadrilateral and angles.

Second Ajima-Malfatti Point
Interactive illustration.

Ajima-Malfatti Point

Animated angle

Lemoine Theorem

Animated angle

Menelaus' Theorem

Animated angle

Triangle and Squares 18  Sangaku Problem

Triangle and Squares 17

Blanchet Theorem

Animated angle

Sawayama -Thebault's theorem

Proposed Problem 33.
Triangle and quadrilateral.

Cyclic Quadrilateral: Ratio of the Diagonals

Problem 32.
Triangle, Cevian, Incircles, Tangents.

Problem 31. Right Triangle, Incircle, Collinears.
Problem 30. Right Triangle, Incircle, Inradius.

Interactive Mind Map of the Van Hiele Model of Geometric Thought

Problem 29.
Right Triangle, altitude, incircle and inradius. Ten conclusions.

Equal Incircle Theorem

 Animated angle

Heron's Formula with medians 

Apollonius' Tangency Problem for Three Circles Interactive illustration.

Problem 29: Geometry Help.
Facts you should know.

Proposed Problem 27
Right Triangle, incircles and inradius.

Proposed Problem 25
Right Triangle, altitude, incircles and inradius

Proposed Problem 23
Right Triangle, altitude, incircles and inradii.

Proposed Problem 22
Right Triangle, altitudes, incircles and inradii.

Proposed problem 19
Right Triangle and Excenter

Proposed problem 20
Right Triangle, incircles and inradii.

Proposed problem 21  Acute triangle, orthocenter, diameter, tangents.