Altitudes and Orthocenter of a Triangle by Mr. Cheung

This GeoGebra example demonstrates how the three altitudes of a triangle meet at the orthocenter and how the orthocenter moves when the vertices are dragged. It covers triangle altitudes, orthocenter, perpendicularity, line segments, intersections, slopes, distances, polygon area relationships, and dynamic geometry. The construction uses Point to create vertices A, B, and C, Polygon to form triangle poly1, Segment to draw sides and altitude lines, Intersect to locate altitude feet or related intersection points D, E, and F, and Slope and Distance to check perpendicular relationships and measure lengths; objects a, b, c, d, e, f and distanceBF support quantitative exploration. Suitable for middle-school geometry, high-school analytic geometry, and classroom demonstrations of triangle centers.