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# Geometry Terms

### Plane Geometry

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

Angle | Formed by two rays, or sides, with a common endpoint called the vertex. |

Acute Angle | The measure of the angle is greater than 0° and less than 90°. |

Right Angle | The measure of the angle is 90°. |

Obtuse Angle | The measure of the angle is greater than 90° and less than 180°. |

Straight Angle | The measure of the angle is 180°. |

Complementary Angles | Two angles whose measures add to 90°. |

Supplementary Angles | Two angles whose measures add to 180°. |

Adjacent Angles | Angles with a common vertex and a common side, but no common interior points. |

Congruent Angles | Angles that have the same measure. |

Vertical Angles | Nonadjacent angles formed by two intersecting lines. |

Parallel Lines | Lines in a plane that never meet. |

Perpendicular Lines | Lines that intersect at 90° angles. |

Transversal | A line that intersects two or more lines that lie on the same plane. |

Triangle Sum Theorem | The theorem that says the angle measures of a triangle add to 180°. |

Acute Triangle | A triangle with 3 acute angles. |

Right Angle | A triangle with 1 right angle. |

Obtuse Triangle | A triangle with 1 obtuse angle. |

Equilateral Triangle | A triangle with 3 congruent sides and 2 congruent angles. |

Isosceles Triangle | A triangle with at least 2 congruent sides and 2 congruent angles. |

Scalene Triangle | A triangle with no congruent sides and no congruent angles. |

Triangle Inequality Theorem | The theorem states that the sum of any 3 sides of a triangle is greater than the 3rd side. |

Polygon | A closed plane figure formed by 3 or more segments. |

Trapezoid | A polygon with exactly 1 pair of parallel sides. |

Parallelogram | A polygon with 2 pairs of parallel sides. |

Rectangle | A polygon with 4 right angles. |

Rhombus | A polygon with 4 congruent sides. |

Square | A polygon with 4 congruent sides and 4 right angles. |

Midpoint | The point that divides a segment into 2 congruent segments. |

Created by:
allvasquez