CK-12 Foundation
Ck 12: Geometry: Circumference and Arc Length Study Guide
This study guide on circumference and arc length covers key vocabulary, the parts of a circle, and formulas for circumference, area, and arc length. It is available for download with free registration.
CK-12 Foundation
Ck 12: Geometry: Arcs and Angles Study Guide
This study guide on arcs and angles covers key vocabulary, arc measurement in degrees and radians, congruent arcs, bisecting arcs, and the angles on, inside, and outside a circle. Also covers formulas and theorems. It is available for...
Thinkport Education
Math by Design: Circumference and Area of a Circle [Pdf]
Young scholars will discover how to estimate and measure the circumference and area of a circle.
National Council of Teachers of Mathematics
Nctm: Illuminations: Power of a Point
Use this tool to investigate what happens when point P is moved to various points within, on, and outside the circle. Can you identify any relationships among the segments and radius?
Geometry Help
Geometry Help: Arcs, Angles, and Sectors
Explains the basic concept of arcs, angles, and sectors with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
Khan Academy
Khan Academy: Inscribed Angles
Practice the relationship between inscribed & central angles that are subtended by the same arc length.
Math Open Reference
Math Open Reference: Angle Measure of an Arc
Learn about the angle measure of an arc with this handy reference tool. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
Khan Academy
Khan Academy: Radians & Arc Length
Solve problems related to radians and arc length like finding an arc length given the central angle and radius.
CK-12 Foundation
Ck 12: Interactive Geometry: 8.9 Arc Length
Recall that a portion of a circle is called an arc. One way to measure an arc is with degrees.
Cuemath
Cuemath: What Is a Radian?
A comprehensive guide for learning all about radians with definitions, formulas, the arc length formula, angles, the circumference, the radius, solved examples, and practice questions.
Wolfram Research
Wolfram Math World: Apothem
MathWorld offers a definition of the apothem of a circle as well as an illustration is provided on this page. An equation is also provided to calculate the apothem of a circle given the radius and the sagitta.
Wolfram Research
Wolfram Math World: Radius
This math site from MathWorld.com defines radius in terms of both a circle and a sphere. The site includes a diagram and links to related topics.
Wolfram Research
Wolfram Math World: Circumference
This site provides the formula for circumference. Links are provided.
Sophia Learning
Sophia: Finding the Area of a Sector Using the Central Angle: Lesson 2
This lesson explains how the central angle can be used to determine the area of a sector and presents several practice problems. Includes answers and a short quiz. It is 2 of 5 in the series titled "Finding the Area of a Sector Using the...
ClassFlow
Class Flow: Spheres Geometry
[Free Registration/Login Required] In this flipchart, students develop an understanding of the properties of a sphere and determine its area and volume.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Circumference
Find a quick, concise explanation of circumference. The formula for finding the circumference of a circle is explained.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Radius
Find a quick, concise explanation of what a radius is. An example is given and clearly explained.
ClassFlow
Class Flow: Circles and Angles
[Free Registration/Login Required] In this flipchart students practice identifying parts of a circle, measure angles, and practice solving area and circumference problems.
Shmoop University
Shmoop: Basic Geometry: Area Formulas
The geometry resource investigates the area of polygons, triangles, circles, and squares. Formulas, examples, and practice exercises are included.
Sophia Learning
Sophia: Sector Area of a Circle: Lesson 2
This lesson will demonstrate how to find the area and radius of a circle when given the sector area and central angle measure. It is 2 of 8 in the series titled "Sector Area of a Circle."
Sophia Learning
Sophia: Sector Area of a Circle: Lesson 4
This lesson will demonstrate how to find the area and radius of a circle when given the sector area and central angle measure. It is 4 of 8 in the series titled "Sector Area of a Circle."
Walter Fendt
Walter Fendt: Thales' Circle
A short interactive activity to prove that a triangle inscribed in a semicircle is right-angled.
Interactive Mathematics
Interactive Mathematics: Applications of Radian Measure
After demonstrating how to find arc length and sector area using radian measures, student can practice the concepts with the examples provided and play an interactive game involving angular velocity.
Calculator Soup
Calculator Soup: Circle Calculator
Use this circle calculator to find the area, circumference, radius, or diameter of a circle. Given any one variable A, C, r or d of a circle you can calculate the other three unknowns.