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Miquel's Theorem


MiquelsTheorem

If a points A^', B^', and C^' are marked on each side of a triangle DeltaABC, one on each side (or on a side's extension), then the three Miquel circles (each through a polygon vertex and the two marked points on the adjacent sides) are concurrent at a point M called the Miquel point. This result is a slight generalization of the so-called pivot theorem.

If M lies in the interior of the triangle, then it satisfies

∠P_2MP_3=180 degrees-alpha_1
(1)
∠P_3MP_1=180 degrees-alpha_2
(2)
∠P_1MP_2=180 degrees-alpha_3.
(3)

The lines from the Miquel point to the marked points make equal angles with the respective sides. (This is a by-product of the Miquel equation.)

MiquelPointLines

A generalized version of Miquel's theorem states that given four lines L_1, ..., L_4 each intersecting the other three, the four Miquel circles passing through each subset of three intersection points of the lines meet in a point known as the 4-Miquel point M. Furthermore, the centers of these four Miquel circles lie on a circle C_4 (Johnson 1929, p. 139). The lines from M to given points on the sides make equal angles with respect to the sides.

Moreover, given n lines taken by (n-1)s yield n Miquel circles like C_4 passing through a point P_n, and their centers lie on a circle C_(n+1).


See also

Clifford's Circle Theorem, Miquel Circles, Miquel Five Circles Theorem, Miquel Equation, Miquel Point, Miquel Triangle, Nine-Point Circle, Pedal Circle, Pivot Theorem

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References

Ayme, J.-L. "A Purely Synthetic Proof of the Droz-Farny Line Theorem." Forum Geom. 4, 219-224, 2004. http://forumgeom.fau.edu/FG2004volume4/FG200426index.html.Honsberger, R. "The Miquel Theorem." Ch. 8 in Episodes in Nineteenth and Twentieth Century Euclidean Geometry. Washington, DC: Math. Assoc. Amer., pp. 79-86, 1995.Johnson, R. A. Modern Geometry: An Elementary Treatise on the Geometry of the Triangle and the Circle. Boston, MA: Houghton Mifflin, pp. 131-144, 1929.Kimberling, C. "Transfigured Triangle Geometry." Preprint. Mar. 5, 2005.Miquel, A. "Mémoire de Géométrie." Journal de mathématiques pures et appliquées de Liouville 1, 485-487, 1838.Wells, D. The Penguin Dictionary of Curious and Interesting Geometry. London: Penguin, pp. 151-152, 1991.

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Miquel's Theorem

Cite this as:

Weisstein, Eric W. "Miquel's Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/MiquelsTheorem.html

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