Merriam-Webster
Merriam Webster: Dictionary Illustration: Types of Triangles
A labeled illustration of six different types of triangles.
OER Commons
Oer Commons: Pre Assessment
Students solve for missing angle measures by applying what they have learned about types of angles and the angle measures of polygons. Students do a pre-assessment at the end of the lesson.
Better Lesson
Better Lesson: Tri, Tri, Tri Angle!
Kindergarteners love to identify shapes in their environment. In order effectively do that, they must be able to recognize different shapes by their specific attributes. In this lesson kindergartners learn about different types of...
Mocomi & Anibrain Digital Technologies
Mocomi: Types of Triangles
Explore the different types of triangles and other properties.
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."
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.
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.
CK-12 Foundation
Ck 12: Angle Bisectors in Triangles
[Free Registration/Login Required] Students will use interactive triangles to explore how a line bisects an angle. Click learn more to watch a video and click challenge me to answer a practice question.
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...
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...
Mathigon
Mathigon: Geometry: Polygons and Polyhedra: Polygons
This lesson focuses on polygons; a polygon is a closed, flat shape that has only straight sides. Polygons can have any number of sides and angles, but the sides cannot be curved.
The Math League
The Math League: Figures and Polygons
This site provides definitions of different types of polygons and figures.
CK-12 Foundation
Ck 12: Geometry: Polygons Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide focuses on polygons: convex vs concave, interior and exterior angles, and basic terminology for common polygons.
Math Open Reference
Math Open Reference: Polygons
Get the definition and properties of a polygon. Then explore such topics as: 1) types of polygon 2) area 3) Perimeter 4) angles associated with polygons and 5) names of polygons.