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# Ch4 Vocabulary

### Triangle Vocabulary

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

Acute Triangle | A triangle where ALL angles are acute (less than 90 degrees) |

Obtuse Triangle | A triangle where one angle is obtuse (greater than 90 degrees but less than 180 degrees) |

Right Triangle | A triangle where one angle is right (EQUAL to 90 degrees) |

Equilateral Triangle | A triangle where all sides are congruent |

Scalene Triangle | A triangle where all three sides have different lengths |

Isosceles Triangle | A triangle with two sides congruent |

Base Angles | the two angles of an isosceles triangle formed by the base and one of the congruent sides (‘bottom angles’) |

Vertex Angle | the angle of an isosceles triangle formed by the congruent sides (‘top angle’) |

Isosceles Triangle Theorem | If two sides of a triangle are congruent, then the triangle is isosceles |

Angle Sum Theorem (aka Triangle Theorem) | The sum of the measures of the interior angles of a triangle is 180 degrees |

Exterior Angle | The angle formed outside of the triangle by extending one side of the triangle out of the triangle |

Remote Interior Angles | The two interior angles of the triangle NOT ADJACENT (next to) the given exterior angle referenced |

Exterior Angle Theorem | The measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles |

Flow Proof | A proof that organizes a series of statements in a logical order starting with given statements. Each statement following includes a reason verifying the statement |

Corollary 4.1 | The acute angles of a right triangle are complementary (their sum is 90 degrees) |

Congruent Triangles | Triangles that are the same size and shape |

CPCTC | Two triangles are congruent if and only if (IFF) their corresponding parts are congruent – Corresponding Parts of Congruent Triangles are Congruent |

Congruence Transformation | to slide, flip or turn a triangle and the size or shape doesn't change |

Included Angle | The angle of a triangle BETWEEN the two given sides of the same triangle |

Included Side | The side of a triangle BETWEEN the two given angles of the same triangle |

Corollary 4.4 (Equilateral Triangle Angle Measures) | Each angle of an equilateral triangle measures 60 degrees |

Created by:
martha.kelley