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The theorem cannot be generalized to all nonplanar triangle-free graphs: not every nonplanar triangle-free graph is 3-colorable. In particular, the Grötzsch graph and the Chvátal graph are triangle-free graphs requiring four colors, and the Mycielskian is a transformation of graphs that can be used to construct triangle-free graphs that ...
An alternative conjecture of Bruce Reed states that high-degree triangle-free graphs must have significantly smaller chromatic number than their degree, and more generally that a graph with maximum degree and maximum clique size must have chromatic number [4] ⌈ + + ⌉.
The Grötzsch graph is a triangle-free graph that cannot be colored with fewer than four colors. Much research about triangle-free graphs has focused on graph coloring. Every bipartite graph (that is, every 2-colorable graph) is triangle-free, and Grötzsch's theorem states that every triangle-free planar graph may be 3-colored. [8]
Ceva's theorem is a theorem of affine geometry, in the sense that it may be stated and proved without using the concepts of angles, areas, and lengths (except for the ratio of the lengths of two line segments that are collinear). It is therefore true for triangles in any affine plane over any field.
Marden's theorem states their location within this triangle more precisely: Suppose the zeroes z 1 , z 2 , and z 3 of a third-degree polynomial p ( z ) are non-collinear. There is a unique ellipse inscribed in the triangle with vertices z 1 , z 2 , z 3 and tangent to the sides at their midpoints : the Steiner inellipse .
Pompeiu's theorem is a result of plane geometry, discovered by the Romanian mathematician Dimitrie Pompeiu. The theorem is simple, but not classical. It states the following: Given an equilateral triangle ABC in the plane, and a point P in the plane of the triangle ABC, the lengths PA, PB, and PC form the sides of a (maybe, degenerate) triangle ...
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From original triangle, ΔA 1 DB 1: Sketch Cayley diagram. Using parallelograms, find A 2 and B 3 O A A 1 DA 2 and O B B 1 DB 3. Using similar triangles, find C 2 and C 3 ΔA 2 C 2 D and ΔDC 3 B 3. Using a parallelogram, find O C O C C 2 DC 3. Check similar triangles ΔO A O C O B. Separate left and right cognate. Put dimensions on Cayley diagram.