The orthocenters of the four components triangles (BCE, ABF, ADE, CDF) of a complete quadrilateral ABCDEF lie on a line called Ortholine or Steiner Line.
Complete quadrilateral ABCDEF is the figure determined by four lines, no three of which are concurrent, and their six points of intersection A, B, D, C, E, and F.
The orthocenter is the intersection of the three altitudes of a triangle.
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Ten problems: 1411-1420
HTML5 and Dynamic Geometry
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