Math2
Math2: Circles
This site has many useful formulas and examples relating to circles, including related definitions, circumference of a circle, area of a circle, length of a circular arc, area of a circular sector, equation of a circle in cartesian...
BBC
Bbc: The Circle
The equation of a circle is the focus of this site. Topics include tangents, intersecting circles, and intersection of lines and circles. Examples and a practice test are available.
Texas Instruments
Texas Instruments: Drawing a Line Tangent to a Circle
Students use the drawing and measurement tools of Cabri Jr. to draw a line tangent to a circle. [Requires Adobe Reader.]
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.
Texas Instruments
Texas Instruments: Chords, Secants, and Tangents
Students 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.
Math Open Reference
Math Open Reference: Parts of a Circle
Learn about parts of a circle with this pictorial index. Click on the diagrams for more information. Includes links to related topics.
Varsity Tutors
Varsity Tutors: Hotmath: Practice Problems: Circle Exercises
Twenty-five problems cover various circle activities. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click the "View Solution" button to check each step of your...
Purple Math
Purplemath: The Unit Circle
Relates the unit circle to the method for finding trig ratios in any of the four quadrants. Demonstrates how the unit circle might be useful.
Khan Academy
Khan Academy: Determining Tangent Lines: Lengths
Solve two problems that apply properties of tangents to determine if a line is tangent to a circle.
Khan Academy
Khan Academy: Determining Tangent Lines: Angles
Solve two problems that apply properties of tangents to determine if a line is tangent to a circle.
Khan Academy
Khan Academy: Challenge Problems: Radius & Tangent
Solve two challenging problems that apply properties of tangents to find the radius of a circle with a tangent.
Math Planet
Math Planet: Geometry: Advanced Information About Circles
Provides advanced information about circles through the use of examples and a brief video lesson. [1:00]
Mathigon
Mathigon: Geometry: Circle and Pi: Degrees and Radians
Rather than dividing a circle into some number of segments (like 360 degrees), mathematicians often prefer to measure angles using the circumference of a unit circle - a circle with radius 1. This way of measuring angles is called...
Mr. Martini's Classroom
Mr. Martini's Classroom: Circles Geometry Review
This resource provides two levels of multiple choice questions to review the parts of a circle as well as area and perimeter.
Khan Academy
Khan Academy: Algebra Ii: Trig Values of Special Angles
Find the sine and cosine of special angles, which are angles whose trig values we can determine without the use of a calculator. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or...
Illustrative Mathematics
Illustrative Mathematics: G C Mutually Tangent Circles
Three circles are mutually tangent. Students are asked to find the total area of the circles plus the area inside where they meet. Students will need to know how to calculate the area of a circle, a sector of a circle, and an equilateral...
Illustrative Mathematics
Illustrative Mathematics: G C Tangent to a Circle From a Point
This task builds on a previous one called ''Right triangles inscribed in circles I.'' Here students are asked to construct a tangent line to a circle from a point outside of the circle. Aligns with G-C.A.4.
Cut the Knot
Cut the Knot!: Monge's Theorem of Three Circles and Common Tangents
Very good site presenting a Trig problem dealing with tangents lines and circles, then linking the student to the solution
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.
Illustrative Mathematics
Illustrative Mathematics: G Srt Tangent Line to Two Circles
The purpose of this task is to use similar triangles and setting up a proportion in order to calculate a side length. Aligns with G-SRT.B.5.
Oswego City School District
Regents Exam Prep Center: Unit Circle
Two hands-on lab activities for instructors to use when teaching about the coordinate graphs of the sine, cosine, and tangent functions derived from a unit circle. The graphs of the reciprocals of the three functions are investigated....
Math Open Reference
Math Open Reference: Circles
A complete reference guide to circles including parts, angles, and arcs. It provides definitions and interactive activities that enhance further explanation.
Analyze Math
Analyze Math: Unit Circle and Trigonometric Functions
The free mathematics tutorial explores the unit circle and trigonometric functions. The tutorial consists of definitions and examples with solutions. The interactive applet allows students to investigate domain, range, and asymptotes of...
University of Vienna (Austria)
The Graphs of Sin, Cos, and Tan Maths Online
This applet allows the user to create the graphs of sin, cos, and tan by moving a scroll bar. The user can watch the unit circle and the graph simultaneously to see how the two are related. The user may also choose to see the angle...