acute angle | | a flat surface that has no thickness |

angle bisector | | a ray that divides an angle into two congruent coplanar angles |

collinear points | | distance and direction from the origin of a number line |

congruent angles | | a 180 degree angle |

congruent segments | | an angle between 90 and 180 degrees |

conjecture | | a 90 degree angle |

coordinate | | angle with the same measure |

coplanar | | part of a line consisting of two endpoints and all points between them |

counterexample | | noncoplanar lines |

inductive reasoning | | coplanar lines that do not intersect |

obtuse angle | | points that lie on the same line |

parallel lines | | an accepted statement of fact |

parallel planes | | a line, segment, or ray that is perpindicular to the segment at its midpoint |

perpindicular bisector | | part of a line consisting of one endpoint and all the points of the line on one side of the endpoint |

perpindicular lines | | reasoning based on patterns one observes |

plane | | points (or lines) that are in the same plane |

postulate | | a conclusion reached using inductive reasoning |

ray | | planes that do not intersect |

right angle | | a positive angle less than 90 degrees |

segment | | two segments with the same length |

skew lines | | two lines that intersect to form right angles |

straight angle | | an example for which the conjecture is incorrect |