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# Geometry Terms

### definitions

Term | Definition |
---|---|

Undefined Terms | Words, usually readily understood, that are not formally explained by means of more basic words and concepts. The basic undefined terms of geometry are point, line and plane. |

Length | The measurement of an object from point A to point B. |

Polygon | Closed figure formed by a finite number of coplanar segments called sides such that the following conditions are met: 1. The sides that have a common endpoint are noncollinear. 2. Each side intersects exactly two other sides, but only at the vertices. |

Reflection | A transformation representing the flip of a figure over a point, line or plane. When in a line it is a function that maps a point to its image compared to its pre-image. |

Translation | A transformation that moves a figure the same distance in the same direction. This function maps each point to its image along a vector so each segment joining a point and its image has the same length as the vector, and is also parallel to the vector. |

Rotation | A transformation that turns every point of a pre-image through a specified angle and direction about a fixed point, called the center of rotation. |

Symmetry | When there exists a rigid motion--reflection, translation, rotation or glide reflection--that maps the figure onto itself. |

Compositions of Transformation | The resulting transformation when a transformation is applied to a figure and then another transformation is applied to its image. |

Congruence | A mapping for which a geometric figure and its image are congruent. |