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# U 1, Lsn 3 Triangles

### Vocabulary

Question | Answer |
---|---|

Alternate Interior Angles Theorem (Alt. Int.) | If two parallel lines are cut by a transversal, then each pair of alternate interior angles are congruent |

Acute Angle | An angle with measure less than 90 degrees |

Triangle Sum Theorem | The sum of the interior angles of a triangle is 180 degrees |

Vertical Angles | Angles formed by two crossing lines and have equal measure, they are across from each other |

Exterior Angle | Angle outside the triangle and have measure equal to the two remote interior angles of the triangle |

Centroid | A point of concurrency inside the triangle where the three medians meet and is the balancing point of the triangle |

Median | A line segment that has one end point at the midpoint of a triangle side and connects to the opposite vertex |

Midsegment | A segment that forms when connecting the two midpoints of two sides of a triangle and has equal measure to 1/2 the parallel side |

Isosceles Triangle | A triangle with two sides congruent |

Congruent | Equal shape and size - used to describe geometric figures and concepts (like the word 'equal' is used in regular math) |

Opposite | Means 'Across from' in math class |

Adjacent | Means 'Next to' |

Equilateral triangle | A triangle with all sides and angles congruent |

CPCTC | Corresponding Parts of Congruent Triangles are Congruent |

SAS | If two sides and an included angle of one triangle are congruent to two sides and an included angle of another triangle, then the two triangle are congruent |

SSS | IF the sides of one triangle are congruent to the sides of a second triangle, then the triangles are congruent |

ASA | If two angles and the included side of one triangle are congruent to the two angles and included side of another triangle, then the two triangles are congruent |

AAS | If two angles and the non-included side of one triangle are congruent to the two angles and non-included side of another triangle, then the two triangles are congruent |

Naming Angles | Used when identifying an angle, the vertex comes in the middle between the two endpoints |