Maths Challenge
Maths challenge.net: Maximum Square
A challenging proof like geometry of finding the square inscribed in a triangle.
That Quiz
That Quiz: Practice Test: Triangles
Test your knowledge on the attributes of triangles. There are eleven levels that may be completed with or without a timer.
University of Georgia
University of Georgia: An Elementary Application of Similar Triangles
Excellent review site on similar triangles. Includes diagrams and explanation of application.
Oswego City School District
Regents Exam Prep Center: Similarity of Triangles
Discover the world of "similarity" in this test prep tutorial on similar triangles. Detailed explanation of concept with examples, challenging interactive practice, and a classroom activity that integrates math and science.
Mathigon
Mathigon: Geometry: Triangles and Trigonometry: Properties of Triangles
This lesson focuses on the properties of triangles, a closed shape that has three sides, three vertices, and and three internal angles. There are different types of triangles such as a right triangle, obtuse, and acute based on the...
Cuemath
Cuemath: Midsegment of a Triangle
This mini-lesson explores the world of the midsegment of a triangle by finding the answers to questions like what is midsegment of a triangle, triangle midsegment theorem, and proof with the help of interactive questions.
OER Commons
Oer Commons: Mars: Proving the Pythagorean Theorem
This lesson is intended to help you assess how well learners are able to produce and evaluate geometrical proofs. PowerPoint slides are included with the lesson.
Wolfram Research
Wolfram Math World: Acute Triangle
This MathWorld site gives a short discussion on acute triangles with links to related terms and topics. The site offers a discussion on the least number of acute triangles to compose various polygons, and a discussion on the relationship...
Texas Instruments
Texas Instruments: Ratios in Right Triangles
The study of properties of right triangles is a major topic in mathematics. In this activity, you will investigate three common right triangle trigonometric ratios. [Requires Adobe Reader.]
Texas Instruments
Texas Instruments: Triangles
This file contains questions related to triangles. The questions can be used to asses your students' understanding of this topic in geometry.
Texas Instruments
Texas Instruments: Angle Theorem
Students use the Cabri Geometry II Plus software to investigate the relationship between angle and ratio in a right triangle.
Texas Instruments
Texas Instruments: Right Triangles Are Cool Because of Pythag's Rule
In this activity, students use the Geoboard to determine the length of the sides of a right triangles. [Requires Adobe Reader.]
Texas Instruments
Texas Instruments: Right Triangle Trig
This is a way to use the TI-Navigator to check for an understanding of sin, cos, and tan before you move onto word problems.
Texas Instruments
Texas Instruments: The Orthocenter of a Triangle
Students understand that the orthocenter is the point of concurrence of the three altitudes of a triangle. They construct circumcircles and Feuerbach circles and determine the relationship between them.
Texas Instruments
Texas Instruments: Triangle Sum
This activity is used to discover that the sum of the measures of the triangle angles is constant and to discover ways of proving the theorem listed in the activity.
Analyze Math
Analyze Math: Special Triangles Used in Trigonometry
The trigonometry tutorial investigates special triangles. The activity includes isosceles right triangles and 30-60-90 triangles. The examples show how to obtain the six trigonometric ratios of the special angles using special triangles.
Analyze Math
Analyze Math: Similar Triangle Problems
The geometry tutorial investigates similar triangles. The activity has several examples with detailed solutions.
Analyze Math
Analyze Math: Congruent Triangle Problems
The geometry tutorial investigates congruent triangles. The activity has several examples with detailed solutions.
Ministry of Education and Universities of the Region of Murcia (Spain)
Ministerio De Educacion Y Ciencia: El Teorema De Pitagoras
Interactive resources and activities that could be used in the classroom either as an introduction or review to a unit dealing with the Pythagoras Theorem. [Requires Java.]
Ministry of Education and Universities of the Region of Murcia (Spain)
Ministerio De Educacion Y Ciencia: Triangulos Semejantes
Learn how to recognize and construct similar triangles with these interactive activities.
Math Open Reference
Math Open Reference: Similar Polygons and Triangles
A complete reference guide to similar triangles and polygons. It provides definitions and interactive activities that enhance further explanation.
Maths Challenge
Maths challenge.net: Corner Circle
This is a "three star" geometry problem where prior knowledge of circles and triangles is recommended to solve this circle in the corner problem.
Other
Trig Without Tears: Solving Triangles
This page provides a good explanation of how to solve oblique triangles (triangles containing no right angles.) The Law of Cosines section is about halfway of the way down the page.
Math Planet
Math Planet: Geometry: Congruent Triangles
Features a definition and a video lesson on congruent triangles with examples. [1:11]