Texas Instruments
Texas Instruments: Angles Formed by Intersecting Chords, Secants, and Tangents
In this activity, students will investigate properties of angles and arcs formed when chords, secants, and tangents intersect and intercept arcs in a circle. They discover several important theorems concerning circles and arc sizes. They...
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...
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.