This web page shows an easy to follow process for constructing a line tangent to a circle from a given point on the outside of the circle.
Sonoma State University, Dr. Steve Wilson

A helpful scientific calculator that runs in your web browser window.
Holt Online Learning

Gives examples of problems with intercepted arc, central angle, and angles inside and outside the circle.
Online Math Learning

This shows examples of problems dealing with circles and tangents
Geometry Expressions

Definition and properties of a tangent
Math Open Reference

This gives an explination of a tangent line to a circle and gives different conjectures. It also gives an interactive sketch pad demonstration.
The Geometry Center

Statements of 3 theorems, with a diagram, and an example for each.
Regents math

This page shows the properties of tangents circumscribing a circle and gives users several practice problems with worked solutions.
Math Warehouse

An interactive explanation of the mathematical relationship between two secants that intersect outside the circle. Also explained is the relationship between a tangent and secant that intersect.
Math Open Reference
