Curated OER
Tantalizing Tangrams
Fourth graders participate in what is considered to be a model lesson. The lesson focuses upon polygons and basic geometry. The lesson addresses national standards and displays how others should be done.
Oswego City School District
Regents Exam Prep Center: Isosceles Triangle Theorem
Material to supplement instruction on isosceles triangles: a lesson with related theorems and examples; an online practice quiz for students to take and check their answers; and guidelines for proving the isosceles triangle theorem.
Khan Academy
Khan Academy: Find Angles in Isosceles Triangles
Find missing angles in isosceles triangles given just one angle. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
CK-12 Foundation
Ck 12: Geometry: Isosceles Triangles
[Free Registration/Login may be required to access all resource tools.] Apply the properties of isosceles triangles.
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.
Texas Instruments
Texas Instruments: Isosceles Triangles
Questions on the basic characteristics of an isosceles triangle
CK-12 Foundation
Ck 12: Elem Math: Determining the Unknown Angle in an Isosceles Triangle
[Free Registration/Login may be required to access all resource tools.] Students watch a video and attempt practice problems on finding the missing angle in an isosceles triangle.
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.
National Council of Teachers of Mathematics
Nctm: Illuminations: Isosceles Triangle Area
Explore when an isosceles triangle obtains its maximum area.
Khan Academy
Khan Academy: Use Pythagorean Theorem to Find Isosceles Triangle Side Lengths
Find the missing side lengths of isosceles triangles by using the Pythagorean Theorem. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video, or receive hints.
National Council of Teachers of Mathematics
The Math Forum: Triangle Formulas
Investigate the geometric definitions of triangles, focusing upon equilateral, isosceles, right, and scalene with detailed drawings and appropriate formulas for each. This site has links to more information on triangles.
Texas Instruments
Texas Instruments: Isosceles Triangle
In this activity, students construct isosceles and equilateral triangles. They discover that if two sides of a triangle are congruent, then the angles opposite them are congruent. They understand that an equilateral triangle is also...
Math Open Reference
Math Open Reference: Isosceles Triangle
A reference guide to isosceles triangles. It provides a definition and interactive animated activity that enhances further explanation. Includes links to related topics.
Wolfram Research
Wolfram Mathworld: Isosceles Triangle
MathWorld explains what an isosceles triangle is and how it compares with equilateral, and scalene triangles. The altitude and area of these triangles are also discussed.
Illustrative Mathematics
Illustrative Mathematics: 8.g Finding Isosceles Triangles
This task asks students to examine three triangles in the coordinate plane and explain why they are isosceles triangles. Aligns with 8.G.B.8.
Mangahigh
Mangahigh: Shape: Isosceles Triangles Inside Circles
Determine isosceles triangles inside a circle made from chords and radii.
CK-12 Foundation
Ck 12: Isosceles Triangles
[Free Registration/Login Required] Students are given an Isosceles triangle and are asked to move the point on the line segment to explore how the angle measure changes. Click learn more to watch a video demonstration and click challenge...
Rice University
Rice University: Cynthia Lanius: Isosceles Triangle Puzzler
This site directs the student to answer true or false questions about isosceles triangles and explain their answers.
Oswego City School District
Regents Exam Prep Center: Angles and Triangles
On this site a viewer can learn about the different types of triangles, and categorized by either angles or sides. Tutorials are also included for interior and exterior angles of triangles. A teacher resource page includes a lesson plan...
Beacon Learning Center
Beacon Learning Center: Triangles Side by Side
This comprehensive web lesson describes how to classify triangles by their angle and side measurements. It provides real-world examples and exercises for students to practice the skill.
Illustrative Mathematics
Illustrative Mathematics: G C Right Triangles Inscribed in Circles I
This task provides a good opportunity to use isosceles triangles and their properties to show an interesting and important result about triangles inscribed in a circle with one side of the triangle a diameter. The fact that these...
Calculator Soup
Calculator Soup: Isosceles Triangles Calculator
Use this calculator to find the sides, perimeter, area, semiperimeter, and altitude of an isosceles triangle.
Free Math Help
Free Math Help: Isosceles Triangles
Students learn about isosceles triangles. The tutorial consists of definitions and sample exercises with solutions.
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