Altitude Applet
(Applet on its own page) Explore the altitude and base of triangles with this interactive applet.

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Definition: an altitude is a segment from the vertex of a triangle to the opposite side and it must be perpendicular to that segment (called the base).
As the picture below shows, sometimes the altitude does not directly meet the opposite side of the triangle. Instead, the altitude intersects the projection of the opposite side.
(Applet on its own page) Explore the altitude and base of triangles with this interactive applet.
