Unit Plan
Khan Academy

Khan Academy: Area and Circumference of Circles Challenge

For Students 6th - 8th
Practice interesting area and circumference problems. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
Unit Plan
Khan Academy

Khan Academy: Circumference of a Circle

For Students 6th - 8th
Find the circumference of a circle when given either the radius or diameter.Find the radius or diameter of a circle when given the circumference.Students receive immediate feedback and have the opportunity to try questions repeatedly,...
Website
National Council of Teachers of Mathematics

The Math Forum: Elementary Geometry Circles

For Students 9th - 10th Standards
The Math Forum offers an archive of question and answer sessions on circles and how they relate to geometry.
Activity
Texas A&M University

Wtamu Virtual Math Lab: Beginning Algebra: Formulas

For Students 9th - 10th
This tutorial will show you how using formulas can help you solve problems. Include formulas for various geometric shapes and steps showing how to use them.
Website
Cool Math

Coolmath: Precalculus Basic Formulas to Know

For Students 9th - 10th Standards
This CoolMath resource provides an introduction to some Precalculus formulas.