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

In this Early Edge video lesson, you'll learn more about Triangles: Perimeter and Area, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

In this Early Edge video lesson, you'll learn more about Equilateral, Isoceles and Scalene Triangles, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

In this Early Edge video lesson, you'll learn more about Triangles, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

In this Early Edge video lesson, you'll learn more about Types of Angles, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

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
