Fermat-Punkt
[color=#000000][b] Gibt es in jedem Dreieck einen Punkt F so, daß die Summe der Entfernungen von F zu den drei Eckpunkten minimal ist?[br] [/b]Diese Problemstellung taucht zum ersten Mal um die Mitte des 17. Jahrhunderts auf. Urheber ist der französischer Mathematiker, Jurist und Parlamentsrat [url=http://www-history.mcs.st-andrews.ac.uk/history/Mathematicians/Fermat.html]Pierre de Fermat [/url] (1601-1665). [br][color=#444444][color=#000000][u]Konstruktion des Fermat-Punkts:[/u][/color][/color][br]● Über den Seiten eines beliebigen Dreiecks ([i]Innenwinkel ≤ 120°[/i]) werden gleichseitige Dreiecke errichtet und deren freie Eckpunkte mit den gegenüberliegenden Eckpunkten des Ausgangsdreiecks verbunden.[/color][br][color=#000000]● Wenn ein Dreieck einen [i]Winkel[/i] von [i]mehr als 120 °[/i] hat, befindet sich der Fermat-Punkt am stumpfen Winkel.[/color][br]
Bernat Link:[url=https://www.geogebra.org/material/show/id/wksuzsqc] https://www.geogebra.org/material/show/id/wksuzsqc[/url][br]zu einem sehr schönen Applet mit einer Illustration auf einer zweidimensionalen Oberfläche
Euler-Gerade und Feuerbach-Kreis
eine dynamische Konstruktion
2D Dynamic construction for studying the properties of the geometric center.
This applet presents a dynamic construction for studying the properties of the [color=#ff00ff]centroid[/color] or [color=#ff00ff]geometric center[/color] [url=https://en.wikipedia.org/wiki/Centroid]https://en.wikipedia.org/wiki/Centroid[/url] .[br][color=#333333]The centroid or Geometric Center [/color]of figure is the arithmetic mean position [math]\vec{P_i}[/math] of all n- points in the figure:[br] [math]\vec{C_m}=\frac{\sum\vec{P_i}}{n},i=1,...,n[/math]. Two special expressions are associated with centroid.[br] - From its definition: [math]\sum\left(\vec{C_m}-\vec{P_i}\right)=0[/math] : The Addition of radius vectors of all points relative to the centroid is zero.[br] - Difference of the two sums: over the squared distances for all points from B and from the centroid is equal to the n times squared distance between centroid and B. It follows, that the sum of the squared distances for all points from the centroid [math]C_m[/math] is the smallest. You can compare results with the Steiner's theorem in the case of unit point masses. [url=https://en.wikipedia.org/wiki/Parallel_axis_theorem]https://en.wikipedia.org/wiki/Parallel_axis_theorem[/url] [br] Creation of this applet was inspired by alfinio [url=https://www.geogebra.org/material/show/id/DZbG9HMZ— February 26, 2015 - 11:36 PM]https://www.geogebra.org/material/show/id/DZbG9HMZ— February 26, 2015 - 11:36 PM[/url] to prove and implement it for more general case.[br] Change the number of particles n in a system, the position of points P[math]_i[/math], B. Make sure that the formula is correct and try again.[br]
2D. Explanation of Invariance of the sum of squares of distances by using the Steiner theorem.
n/2 points of [color=#0000ff]A[sub]1[/sub],...,A[sub]n[/sub][/color] may be moving in a circle of radius r. Each [color=#0000ff]point[/color] has [color=#ff7700]antipodal point[/color] on the circle. Thus, the center of gravity [color=#ff00ff]Cm[/color] is the centre of the circle. [br] It is shown, that the sum of squares of distances from any point [color=#ff0000]D[/color] of a circle to → {[color=#0000ff]A[sub]i[/sub][/color] } , divided by radius squared, is always equal of twice the number of points. [br][url=https://en.wikipedia.org/wiki/Parallel_axis_theorem]https://en.wikipedia.org/wiki/Parallel_axis_theorem[/url][br][url=https://en.wikipedia.org/wiki/Antipodal_point]https://en.wikipedia.org/wiki/Antipodal_point[/url]