A | B |

acute triangle | all angles less than 90 degrees |

adjacent interior angles | angle within a triangle that's next to the exterior angle |

base of a triangle | the bottom side |

collinear points | three in a row form a line |

conclusion | the ending statement in a proof |

coordinate plane | x-y axis and all points on them |

equiangular triangle | all three angles are equal |

equilateral triangle | all three sides are equal |

exterior angle | formed by extending one side of the triangle |

given | facts in a proof that you begin with |

indirect reasoning | list all the possible solutions, then show that all but one are impossible |

isosceles triangle | two sides are equal |

noncollinear points | points not on the same line |

obtuse triangle | one angle is greater than 90 degrees |

ordered pair | point on the (x,y) plane |

origin | point of interesection on a plane (0,0) |

parallel lines | two lines that run next to each other and never cross |

postulate | statement assumed to be true in all cases |

remote interior angles | the sum of two remote interior angles equals the exterior angle |

right triangle | one angle equals 90 degrees |

scalene triangle | none of the sides are equal |

slash mark (tick mark) | shows equal angles or sides |

theorem | statement found true in all cases due to deductive reasoning |

triangle | figure consisting of 3 noncollinear points and their connecting line segments |

triangle inequality | the difference of the sides < x < the sum of the sides |

two-column proof | statements in one column and the reasons in another |

x-coordinate | the first number in an ordered pair; runs horizontal |

y-coordinate | the second number in an ordered pair; runs vertical |