An altitude is the segment or line through a vertex that is perpendicular to the opposite side.
In the applet above, construct the altitude from point A. Use the geometry tools to construct a line perpendicular to BC through A. [br]--Move the vertices around to make different types of triangles. [br]1) What do you notice about the altitude?[br]--Construct altitudes through the other two vertices.[br]2) What do you notice about the three altitudes?
The point of concurrency for the altitudes of a triangle is called the orthocenter.