Walter Fendt
Walter Fendt: Thales' Circle
A short interactive activity to prove that a triangle inscribed in a semicircle is right-angled.
Math Words
Mathwords: Inscribed Circles
Mathwords provides an explanation and a diagram of an inscribed circle. By clicking on any of the highlighted words, you will learn about related terms.
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.
Texas Education Agency
Texas Gateway: Using Logical Reasoning to Prove Conjectures About Circles
Given conjectures about circles, the student will use deductive reasoning and counterexamples to prove or disprove the conjectures.
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 Origami Equilateral Triangle
The purpose of this task is to explore reflections in the context of paper folding. Each fold is associated with a line of reflection and understanding each step in the construction requires careful analysis of angles and of the...
Varsity Tutors
Varsity Tutors: Hotmath: Graphing Calculator Practice Problems: Circles
Practice using your graphing calculator for drawing circles and for finding measurements for circles and parts of the circle. If you get stumped or if you would like to check your work, then select the View Solution button, which is...
Illustrative Mathematics
Illustrative Mathematics: G C, G Co Tangent Lines and the Radius of a Circle
In this task, students are shown a circle with center O and point P on the circle. L is a line that is a tangent to the circle at P. They must show that line OP is perpendicular to line L. Aligns with G-C.A.2, G-CO.A, and G-CO.C.9.
Texas Instruments
Texas Instruments: Chords, Secants, and Tangents
Learners construct chords, secants, and tangents. From those constructions, they develop a deeper understanding of the terms, as well as explore certain properties of the constructions.
Texas Instruments
Texas Instruments: Segments Formed by Intersecting Chords, Secants, and Tangents
This activity is designed to help students discover several important theorems concerning lengths of segments formed by intersecting chords, secants, and tangents.
Illustrative Mathematics
Illustrative Mathematics: G C, G Srt Neglecting the Curvature of the Earth
Jerry and Ashley are trying to find out if it is possible to see the lowest point in the USA from the highest point in the USA. It turns out that the highest point in the United States, the peak of Mount Whitney, is only 85 miles from...
CK-12 Foundation
Ck 12: Geometry: Chords in Circles
[Free Registration/Login may be required to access all resource tools.] In this lesson, students apply chord theorems. Students examine guided notes, review guided practice, watch instructional videos and attempt practice problems.
CK-12 Foundation
Ck 12: Geometry: Segments From Chords
[Free Registration/Login may be required to access all resource tools.] Looks at how to apply the Intersecting Chords Theorem.
Cut the Knot
Cut the Knot: Existence of the Orthocenter
This site defines the altitude of a triangle and gives the standard notation for altitudes of a triangle. The site then goes to list several proofs involving altitudes and orthocenters.
Illustrative Mathematics
Illustrative Mathematics: G C Locating Warehouse
You have been asked to place a warehouse so that it is an equal distance from three roads on a map. Students must fold a paper so that this point is where two folds intersect, and they must explain why their construction works and why...
Math Open Reference
Math Open Reference: Thales' Theorem
Learn about Thales' Theorem with this handy reference guide. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
Khan Academy
Khan Academy: Tangents of Circles Problems
Solve problems related to tangents of circles. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
Khan Academy
Khan Academy: Tangents of Circles Problems
Solve problems related to tangents of circles.
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