Texas Instruments
Texas Instruments: Similar Triangles and Proportions
In this activity, students will investigate the relationship among the similar triangles formed when a segment is constructed parallel to one side of a triangle. They will explore the various ratios that exist between the lengths of the...
Math Is Fun
Math Is Fun: Area of Triangles Without Right Angles
Learn how to find the area of triangles without right angles. Find the formula to use depending on the information you know about the triangle: base and height, three sides, or two sides and an angle.
CK-12 Foundation
Ck 12: Triangle Classification
[Free Registration/Login Required] Students will move the vertices to different points to create different obtuse triangles. Click learn more to watch a video demonstration and click challenge me to answer a practice question.
Oswego City School District
Regents Exam Prep Center: Area of a Triangle and Parallelogram Using Trig
How can trigonometry be used to find the area of a triangle or parallelogram? Does the triangle need to be a right triangle, and how accurate can the results possibly be? The answers to these questions are found here along with several...
Analyze Math
Analyze Math: Area of Triangles
The geometry resource explores the different formulas used to calculate the area of triangles. The applet investigates the angles and sides of a triangle.
University of California
University of California: Triangles and Simplices
This site from the University of California deals with different applications and topics pertaining to triangles, particularly triangulation.
Math Planet
Math Planet: Geometry: Parallelogram, Triangles Etc
Resource examines the area of geometric solids through examples and a video lesson. [0:39]
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...
Illustrative Mathematics
Illustrative Mathematics: G Co Midpoints of Triangle Sides
The goal of this task is to use similarity transformations to relate two triangles. The triangles are obtained by taking midpoints of two sides of a given triangle. Aligns with HSG-CO.C.10.
Illustrative Mathematics
Illustrative Mathematics: G C Circumcenter of a Triangle
The goal of this task is to construct the circumcenter of a triangle, that is, the point which is the same distance from each of the triangle's three vertices. This task shows that the three perpendicular bisectors of the sides of a...
Illustrative Mathematics
Illustrative Mathematics: G Srt Similar Triangles
This task works toward establishing the AA criterion for similarity of triangles. Students are asked to provide a detailed sequence of transformations that moves one of the given triangles onto the other. Aligns with G-SRT.A.3.
Illustrative Mathematics
Illustrative Mathematics: G Srt Finding the Area of an Equilateral Triangle
This task examines how to calculate the area of an equilateral triangle two ways: using triangle congruence and using trigonometric ratios. Aligns with G-CO.C.10 and G-SRT.C.
CK-12 Foundation
Ck 12: Trigonometry: Introduction to the Triangle Area Formula
[Free Registration/Login may be required to access all resource tools.] This lesson covers how to find the area of a triangle using sine.
CK-12 Foundation
Ck 12: Geometry: Inscribed Similar Triangles
[Free Registration/Login may be required to access all resource tools.] Apply the fact that the altitude of a right triangle creates similar triangles.
Other
Gobierno De Navarra: Puntos Y Rectas Notables De Un Triangle
Learn how to construct the bisectors, median and altitude of a triangle.
National Council of Teachers of Mathematics
Nctm: Illuminations: Area of Trapezoids
Investigate how changes in the base and height of a trapezoid affect its area.
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.
Math Open Reference
Math Open Reference: Altitude of a Triangle
Learn about the altitude of a triangle with this handy reference tool. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
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.
CK-12 Foundation
Ck 12: Interactive Geometry: 17.5 Sine to Find the Area of a Triangle
Learn how to sine to find the area of a triangle.
CK-12 Foundation
Ck 12: Interactive Geometry: 4.5 Theorems About Concurrence in Triangles
Find out about some common centers of triangles.
Quia
Ixl Learning: Similar Triangles
Brush up on your math skills relating to similar triangles then try some practice problems to test your understanding.
Khan Academy
Khan Academy: Triangle Similarity Review
Review the triangle similarity criteria and use them to determine similar triangles.
Khan Academy
Khan Academy: Solve Triangles: Angle Bisector Theorem
Use the angle bisector theorem to find missing side lengths in triangles.