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

This interactive site defines a triangle’s centroid, gives interesting facts of a centroid and allows users to manipulate a virtual triangle showing the different positions a centroid can have based on a given triangle.
Math Open Reference

This gives descriptions of each point of concurrency and shows the construction of these points includes links to GPS files for interaction.
An investigation of concurrency

This interactive site defines a circumcenter of a triangle, gives relevant properties of a circumcenter and allows users to manipulate a virtual triangle showing the different positions a circumcenter can have based on a given triangle.
Math Open Reference

A great site with exploration on altitudes, angle bisectors, median, and perpendicular bisectors. Has background information and an interactive example with follow up questions for each section.
Triangle Centers from University of Illinois

This site discusses the defintion of the centroid and median and gives the formulas for the lengths of the medians.
VIAS Encyclopedia

Colorful tutorial with diagrams, explanations and examples.
A Gutierrez

Describes in great detail the concepts of Median, Altitude, Angle Bisector, and Perpendicular Bisector of a triangle, and dicusses their concurrence at the Centroid, Orthocenter, Incenter, and Circumcenter. Also gives an overview of their placement on the Euler Line.
Regents Exam Prep Center

This website shows an animated demonstration for constructing the orthocenter of a triangle using only a compass and straightedge. It also includes stepbystep written instructions for this process.
Math Open Reference

This website shows an animated demonstration for constructing the circumcenter of a triangle, and thus the circumcirlce of the triangle, using only a compass and straightedge. It also includes stepbystep written instructions for this process.
Math Open Reference
