Other
Mathway: Trigonometry Formulas
Resource provides trigonometry formulas for unit circle, reciprocal identities, ratio identities, Pythagorean identities, sum and difference formulas, and double-angle formulas.
Cuemath
Cuemath: Obtuse Triangle
In this mini-lesson, learn about obtuse triangles including the obtuse triangle definition, sides, properties, examples, and other fun facts related to it.
Cuemath
Cuemath: Triangles
Explore everything about triangles. Learn about the different types, important properties, and how to find its area and perimeter. Check out the solved examples and interactive questions for better understanding.
Illustrative Mathematics
Illustrative Mathematics: G Gpe, F Tf Coordinates of Points on a Circle
For this task, students are shown a unit circle in a plane and an angle measured from the x-axis. They must determine the coordinates of the line segment for the angle and answer a question about the sum of the coordinates. The purpose...
Mathigon
Mathigon: Geometry: Triangles and Trigonometry: Pythagoras' Theorem
Pythagoras' Theorem: In any right-angled triangle, the square of the length of the hypotenuse (the side that lies opposite the right angle) is equal to the sum of the squares of the other two sides. (A+B=C)
Math Words
Math words.com: Trig Identities
This MathWords.com site lists the equations for all of the trigonometric identities.
Other
Brown Math: Remembering Trig Identities
Faced with a large number of trigonometric identities, students tend to try to memorize them all. This site the emphasis is on understanding how the functions work and on memorizing only about a half dozen of them - all the others work...
Math Medics
S.o.s. Math: Table of Trigonometric Identities
This tutorial highlights the numerous trigonometric identites (but does not define the basic trigonometric functions).
Lawrence Hall of Science
The Math Page: Trigonometry: Trigonometric Identities
This resource clearly and thoroughly explains the many types of trigonometric identities. There are example problems solved, problems for the student to attempt, and answers to the student problems.
CK-12 Foundation
Ck 12: Interactive Geometry: 4.4 Theorems About Triangles
Discover some theorems about triangles.
Purple Math
Purplemath: The Pythagorean Theorem
Defines the Pythagorean Theorem, and demonstrates how to use this Theorem in connection with right-angled triangles.
Walter Fendt
Walter Fendt: Cyclic Quadrilateral (Inscribed Quadrilateral)
A short interactive activity which allows you to move the vertices of a quadrilateral to prove that the sum of the opposite angles is 180 degrees.
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