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Circle and Pi: online activities, games, and tutorials

This is a hand-picked list of online tools, activities, games, and worksheets about the parts of a circle, area of a circle, and Pi.

Circle / Pi

Circle Worksheets
Customizable worksheets for the area/circumference/radius of a circle.

Area of a Circle, Formula & Illustrated Lesson
The interactive tool shows you the area of the circle as the radius increases. The page also includes a short quiz.

Circle Tool
An applet that allows you to investigate how the area and circumference of a circle compare to its radius and diameter in the Intro and Investigation sections and then hone your skills in the Problems section. You can drag the radius to various lengths, and the click the "Add to Table" button to record the data in the table. You can also examine the ratios of any two measures, and make a graph of the data.

Radius, Diameter, and Circumference
A simple lesson with an interactive quiz about radius, diameter, and circumference of a circle.

The Area of a Circle as a Limit
An animation that illustrates how the area of a circle is a limit of the sum of the areas of interior triangles as the number of triangles goes to infinity. This is the idea I explain in this book (Math Mammoth Geometry 2).

Math Mammoth Geometry 2

A self-teaching worktext for 6th-7th grade that covers the area of triangles, parallelograms, and polygons, pi, area of circle, nets, surface area, and volume of common solids.

Download ($5.70). Also available as a printed copy.

=> Learn more and see the free samples!

See more topical Math Mammoth books

Area of Circle
An activity where you measure a circle and the resulting figure when you cut it into wedges and tape them together to form a crude parallelogram.

Rolling circle illustrating Pi
This is a short animation where a circle with diameter 1 rolls on a number line one complete roll. Of course having rolled once around its circumference, it now lands at 3.14 or Pi.

Dr. Math Introduces Geometry: Learning Geometry is Easy! Just ask Dr. Math!
A supplement to middle school geometry, Dr. Math Introduces Geometry has a light tone, clear layout, and humorous cartoons by Jessica Wolk-Stanley. The best part is that the explanations to math questions are accurate and clear. You'll find answers to dozens of real questions from students who needed help understanding the basic concepts of geometry. This book covers angles, triangles, quadrilaterals, area, perimeter, Pi, circle parts, polyhedra, surface area, volume, nets, congruent transformations, and symmetry. Price ~$12 new, ~$1-6 used.

Geometry worksheets at AGMath.com
Hundreds of free PDF worksheets for high school geometry topics, including geometric constructions, triangle congruence, circle, area, the Pythagorean Theorem, solid geometry, and similarity. The worksheets are loosely based on the "Discovering Geometry" textbook by Michael Serra. Compiled by math teacher Jason Batterson.

Amazing History of Pi
A short and simple introduction to the history of pi.

Math Mammoth Geometry Worksheets Collection
A collection of quality worksheets with variable problems for grades 3-8. Topics include angle relationships, triangles, quadrilaterals, congruency, similar figures, constructions, area, volume, and the Pythagorean Theorem. Price: $9.00 download. See the free samples!
Math Mammoth Geometry Worksheets Collection

Approximating Pi
How did Archimedes find the approximate value of pi? This interactive tool illustrates Archimedes' basic approach with inscribed or circumscribed polygons.

Pi Day Activities & Links
Two pi-related activities to do at home, plus a lot of fun links about pi. Originally meant for Pi Day (celebrated 3/14 each year).

Visualization of the first 4 million digits of Pi
This online visualization represents the first 4,000,000 decimals of Pi within a single image. Each unique digit of Pi corresponds to a specific color, and is rendered as a 1x1 pixel dot. You can also search for the first occurrences of any specific decimal combination.

5 Trillion Digits of Pi
As of August 2010, the world record for computing digits of pi was 5 trillion digits. This will keep changing, of course.


Math Mammoth Geometry 2
A textbook/workbook together for grades 6-7, written by the owner of this site. It continues the study of goemetry after Math Mammoth Geometry 1, continually emphasizing conceptual understanding, besides calculation-type exercises. Price: $5.80 download.

Geometry: A Guided Inquiry
An excellent choice for high school geometry. I've written an in-depth review of this book and of its supplement Home Study Companion - Geometry, latter by David Chandler.

Harold Jacobs Geometry
A popular choice for geometry among homeschoolers, and well written. Please read my review.

Dr. Math Presents More Geometry
An inexpensive companion to any high school geometry course with excellent explanations. Read my review.

Practice makes perfect. Practice math at IXL.com

Free algebra and geometry lessons