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Construct the orthocenter of triangle and three midpoints (say A', B' C' ) between vertices and orthocenter. Construct a circumcircle of A'B'C' . This is the nine-point circle, it intersects each side of the original triangle at two points: the base of altitude and midpoint. Construct an intersection of one side with the circle at midpoint now ...
The dihedral group D 3 is isomorphic to two other symmetry groups in three dimensions: one with a 3-fold rotation axis and a perpendicular 2-fold rotation axis (hence three of these): D 3; one with a 3-fold rotation axis in a plane of reflection (and hence also in two other planes of reflection): C 3v
A triangle in which one of the angles is a right angle is a right triangle, a triangle in which all of its angles are less than that angle is an acute triangle, and a triangle in which one of it angles is greater than that angle is an obtuse triangle. [8]
Various methods may be used in practice, depending on what is known about the triangle. Other frequently used formulas for the area of a triangle use trigonometry, side lengths (Heron's formula), vectors, coordinates, line integrals, Pick's theorem, or other properties. [3]
An auxiliary view or pictorial, is an orthographic view that is projected into any plane other than one of the six primary views. [3] These views are typically used when an object has a surface in an oblique plane. By projecting into a plane parallel with the oblique surface, the true size and shape of the surface are shown.
Let ABC be a plane triangle and let ( x : y : z) be the trilinear coordinates of an arbitrary point in the plane of triangle ABC. A straight line in the plane of triangle ABC whose equation in trilinear coordinates has the form f ( a, b, c) x + g ( a, b, c) y + h ( a, b, c) z = 0. where the point with trilinear coordinates ( f ( a, b, c) : g ...
If a point is on a sideline of the reference triangle, its corresponding trilinear coordinate is 0. If an exterior point is on the opposite side of a sideline from the interior of the triangle, its trilinear coordinate associated with that sideline is negative. It is impossible for all three trilinear coordinates to be non-positive.
The triangle group is the infinite symmetry group of a certain tessellation (or tiling) of the Euclidean plane by triangles whose angles add up to π (or 180°). Up to permutations, the triple (l, m, n) is one of the triples (2,3,6), (2,4,4), (3,3,3). The corresponding triangle groups are instances of wallpaper groups.