Texas Instruments
Texas Instruments: The Orthocenter of a Triangle
Students understand that the orthocenter is the point of concurrence of the three altitudes of a triangle. They construct circumcircles and Feuerbach circles and determine the relationship between them.
Texas Instruments
Texas Instruments: Exploring the Orthocenter of a Triangle
In this activity, students use the Cabri Jr. tools to draw altitudes in a triangle. They construct a line perpendicular to a given line and through a given point. [Requires Adobe Reader.]
Texas Instruments
Texas Instruments: Centers of a Triangle
The centroid, circumcenter, orthocenter, and incenter are the four classic centers of a triangle that are studied in geometry. In this activity, you will construct these center points and discover their properties. [Requires Adobe Reader.]
University of Georgia
University of Georgia: Inter Math: Orthocenter
This site from InterMath gives a description of the orthocenter of a triangle along with a visual representation. Be sure to follow the links to related terms, everyday examples, challenging problems, more information, and the...
Math Words
Math words.com: Altitude of a Triangle
This site provides a definition of what the altitude of a triangle is. It also provides a diagram.
Other
Gobierno De Navarra: Puntos Y Rectas Notables De Un Triangle
Learn how to construct the bisectors, median and altitude of a triangle.
Texas Instruments
Texas Instruments: Centroid and Orthocenter
In this activity, students analyze the location of the centroid and orthocenter for different triangles.
Wolfram Research
Wolfram Math World: Orthocenter
This site from MathWorld provides a diagram of a triangle with its orthocenter labeled. The site details how to find the orthocenter with links to the key terms. The site details many other interesting properties of the triangle...
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Constructing the Orthocenter
Dr. Math shows how to construct the orthocenter of any triangle using a compass and straight edge.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Triangle Altitudes
Here at the Math Forum, Dr. Math proves the concurrency of the altitudes of a triangle. Links are provided for associated topics.
CK-12 Foundation
Ck 12: Altitudes: Orthocenter
[Free Registration/Login Required] Students will use the interactive riangle and points to explore altitudes such as the orthocenter. Click learn more to watch a video and click challenge me to answer a practice question.
Other
University of Evansville: Encyclopedia Triangle Centers
This site contains a comprehensive study of triangle centers. Seems more for an advanced level. Provides a list of six links to 1114 centers.