Congruence. Index.

Similarity, Proportions. Index.
 

Areas Index.

Equilateral Triangle

Isosceles Triangle

Right Triangle Index.

Obtuse Triangle Index.

Median Index.
Theorems and Problems.
 

Altitude Index.
Theorems and Problems.
 

Special Right Triangle 30-60 Index.

Special Right Triangles Index.

Triangle and Squares.
 

Area of a Triangle.Index

Euclid's Elements Book I, 23 Definitions.

Triangle Centers Index.

Incenter.Index
 

Excenter Index

Centroid Index.

Circumcenter Index.

Orthocenter.
 

Napoleon Theorem

Triangle Area Problem.

Equilateral triangle.

Problem 132.Triangle, 60 degree, Orthocenter,

Problem 125. Area of Triangle, Star, Trisection of Sides

Problem 129. Triangle, Concurrent Cevians, Sum of Ratios.

Problem 127. Centroid and Incenter of a Triangle, Parallel, Proportions.

Problem 126. Incenter of Triangle, Angle Bisector, Proportions.

Problem 125. Area of Triangle, Star, Trisection of Sides

Problem 124. Area of triangle, Similarity, Trisection of Sides

Problem 123. Area of triangle, Similarity, Trisection of Sides

Problem 122. Marion Walter's Theorem

Problem 120. Area of triangle, incenter, excircles

Problem 119. Area of triangle, incenter, excircle

Problem 117. Area of triangle, incenter, excircles

Problem 115. Area of triangle, excircles

Intouch and Extouch Triangles, Areas

Contact Triangles Areas, Incircle, Excircle

Contact Triangles Areas, Incircle, Excircle, Inradius, Exradius

Area of the Contact Triangle, inradius, circumradius

Mascheroni Construction with compass alone.

Right Triangles, Formulas and Facts

Mind Map of the Pythagorean Theorem
Proofs by shears, translation, similarity. Facts.

Triangle and Squares 20