Math Open Reference
Math Open Reference: Radius of a Circle
Learn about the radius of a circle with this useful reference guide. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
Mathigon
Mathigon: Geometry: Circle and Pi: Introduction
This lesson focuses on the characteristics of a circle including similarity, radius, circumference, and Pi. It provides formulas to determine the area of a circle, calculating Pi, and learning exercises throughout.
Khan Academy
Khan Academy: Praxis Core Math: Circles Lesson
A basic review of circles and how to calculate the circumference, radius, diameter, and area. Includes practice questions.
Calculator Soup
Calculator Soup: Tube Calculator
This calculator will calculate the various properties of a tube, also called a pipe or hollow cylinder, given 3 known values from variables of radii, circumference, wall thickness and height.
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...
National Council of Teachers of Mathematics
The Math Forum: Pi Day
Need some ideas for Pi Day on March 14th? You can get some great resources at this location. There are all kinds of links available.
University of North Carolina
A Dictionary of Units of Measurement
This site contains an extensive list of various units of measurement known internationally and across several disciplines. Unit symbols are also included.
Illustrative Mathematics
Illustrative Mathematics: G Gmd Area of a Circle
For this task, students investigate and develop an understanding of the formula for the area of a circle. Aligns with G-GMD.A.1.