Khan Academy
Khan Academy: Triangle Similarity Review
Review the triangle similarity criteria and use them to determine similar triangles.
Ministry of Education and Employment of Spain
Red Escolar: Un Triangulo Sorprendente
In Spanish. Different activities which involve the following concepts: right triangles, perpendicular lines, classification of triangles, area of a square and Pythagorean theorem.
Sophia Learning
Sophia: Using Similar Triangles to Make Indirect Measurements
This lesson explains why similar triangles can be used to make indirect measurements, and provides an example.
Free Math Help
Free Math Help: Congruent Triangles
Students learn about congruent triangles. The tutorial consists of definitions and sample exercises with solutions.
Free Math Help
Free Math Help: Classification of Polygons and Triangles
The Geometry session explores the classification of polygons and triangles. Definitions and examples are included.
Shmoop University
Shmoop: Basic Geometry: Triangles
The geometry resource explores triangles. Descriptions, examples, and practice exercises are included.
Shmoop University
Shmoop: Basic Geometry: Similar Figures
The geometry resource explores similar figures. Notes, examples, and practice exercises are included.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Similar Triangles
Find a quick, concise explanation of similar triangles. Examples are given and clearly explained.
National Council of Teachers of Mathematics
Nctm: Illuminations: Triangle Classification
Use this applet to show how the placement of the third vertex of a triangle affects the classification of that triangle.
Wolfram Research
Wolfram Math World: Similar Triangles
Find the necessary information to decide if triangles are similar at this MathWorld site.