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PointSymmetry
We needto definesometermsbeforepointsymmetrycan be defined.
Reflectionin a point:Points and are reflectionsof eachotherin point if and are collinear
and.
In the diagram:
is the reflectionof in point (and vice versa).is the reflectionof in point (and vice versa).A plane(two-dimensional)figurehaspointsymmetryif the reflection(in the center)of everypointon the
figureis also a pointon the figure.
A figurewith pointsymmetrylooksthe sameright side up and upsidedown;it looksthe samefrom the left
and from the right.
The figuresbelowhavepointsymmetry.
Notethat all segmentsconnectinga pointof the figureto its imageintersectat a commonpointcalledthe
center.
Pointsymmetryis a specialcaseof rotationalsymmetry.