David Little
Mathematics Department
Penn State University
Eberly College of Science
University Park, PA 16802
Office: 403 McAllister
Phone: (814) 865-3329
Fax: (814) 865-3735

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An altitude of a triangle is a line segment which has as one of it's endpoints a vertex v of the triangle. It's other endpoint the projection of v onto the side opposite v . In the triangle below, draw the three altitudes. Move the vertices of the triangle around to see how the altitudes are affected. What do you notice?

As you have seen, the three lines containing the altitudes of a triangle intersect at a common point. This point is called the orthocenter.