Khan Academy
Khan Academy: Identify Triangles by Side Lengths
Practice identifying triangles by their side-lengths as equilateral, isosceles, or scalene. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
Geometry Help
Geometry Help: Isosceles Triangles
Explains the basic concept of isosceles triangles with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
K-5 Math Teaching Resources
K 5 Math Teaching Resources: Isosceles Triangles on the Geoboard [Pdf]
Students will learn about isosceles triangles. Materials needed include circular geoboards, rubber bands, circular geoboard paper and rulers.
Texas Instruments
Texas Instruments: Constructing Triangles
This activity focuses on the various ways to construct the different types of triangles such as isosceles, equilateral, right, and right isosceles triangles. Students will begin by constructing triangles based on a minimal definition of...
CK-12 Foundation
Ck 12: Geometry: Isosceles Triangles
[Free Registration/Login may be required to access all resource tools.] This concept will teach students the properties of isosceles triangles and how to apply them to different types of problems.
Science Struck
Science Struck: List of Different Types of Geometric Shapes
A comprehensive list of 2D shapes and 3D solids with everything from a triangle to a dodecahedron. Includes illustrations and short descriptions of attributes for each.
Rice University
Rice University: Geometry Online: Impossible Triangles
This site has an activity that displays several impossible triangles. The rules for triangles are also displayed. The student has to determine which rule has been violated for each impossible triangle.
Illustrative Mathematics
Illustrative Mathematics: G Co Classifying Triangles
The goal of this task is to help students synthesize their knowledge of triangles where only two of the vertices have been given. They will need to know that a triangle inscribed in a circle, with a diameter of the circle as one side, is...
Math Open Reference
Math Open Reference: Obtuse Triangle
A reference guide to obtuse triangles. It provides a definition and interactive animated activity that enhances further explanation.
Math Open Reference
Math Open Reference: Area of an Equilateral Triangle
Learn about the area of an equilateral triangle with this helpful reference tool. Provides a detailed definition, examples, and an internet activity that enhances further explanation. Includes links to related topics.
Math Open Reference
Math Open Reference: Acute Triangle
Explore acute triangles with this handy reference guide. Provides a detailed definition and an interactive activity that enhances further explanation. Includes links to related topics.
E-learning for Kids
E Learning for Kids: Math: Group of Pyramids: 2 D Shapes
Abeni works at the pyramids. Visit her and find out more about circles and triangles.
Sophia Learning
Sophia: Equilateral Triangle Interior Angles Practice Problems: Lesson 5
This lesson will provide practice problems that involve solving for unknown angle and side measures of equilateral triangles. It is 5 of 5 in the series titled "Equilateral Triangle Interior Angles Practice Problems."
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.
Math Is Fun
Math Is Fun: Triangles
Students learn about the terminology and formulas associated with triangles. The learning resource consists of definitions, diagrams, and examples.
Shmoop University
Shmoop: Basic Geometry: Triangles
The geometry resource explores triangles. Descriptions, examples, and practice exercises are included.
National Council of Teachers of Mathematics
The Math Forum: Problems Library Geometry Triangles
This site contains a wealth of problems that deal with the basic definitions of medians, altitudes, angle bisectors, and perpendicular bisectors or the defining characteristics of the different types of triangles. There are also...
ClassFlow
Class Flow: Classifying Triangles
[Free Registration/Login Required] This flipchart introduces students to the different types of triangles and how to classify them.
University of Saskatchewan (Canada)
University of Saskatchewan: Triangles
This site from the University of Saskatchewan provides an explanation of similar triangles, the Pythagorean theorem, and the distance between arbitrary points in a plane. Example problems for each of these concepts are provided.
CK-12 Foundation
Ck 12: Elem Math: Classifying Right Obtuse or Acute by Angle Measure
[Free Registration/Login may be required to access all resource tools.] Students watch a video and attempt practice problems on how to classify triangles based on angle measures.
Homeschool Math
Homeschool Math: Triangles
This lesson plan provides students with an opportunity to practice drawing and measuring triangles and angles. It also shows pictures and gives definitions of each type of angle and triangle.
Science Struck
Science Struck: Similarity Statement in Geometry With Examples
Models how to write a similarity statement about different types of triangles and quadrilaterals.
Sophia Learning
Sophia: Scalene, Isosceles, and Equilateral Triangles: Lesson 1
This lesson will define scalene, isosceles, and equilateral triangles. It is 1 of 5 in the series titled "Scalene, Isosceles, and Equilateral Triangles."
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.
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