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# Geometry LC Maths

### Geometry Ord Level Definitions

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

Plane | Flat two-dimensional surface. It has length and width but no thickness |

Point | Position on a plane |

Coplanar | If points lie on the same plane |

Line | Straight, infinitely thin line that continues forever in both directions; it has no endpoints |

Collinear points | points that lie on the same line |

Perpendicular lines | Lines that are at right angles or 90 degrees to each other |

Parallel lines | Lines that are the same distance apart. They never meet |

Line segment | Part of a straight line. It has two endpoints and can be measured using a ruler |

Ray | Part of a line that originates at a point and goes on forever in only one direction |

Vertex | Where 2 rays meet |

Acute angle | Angle less than 90 degrees |

Right angle | 90 degree angle |

Obtuse angle | angle greater than 90 degrees but less than 180 degrees |

Reflex angle | Angle greater than 180 degrTees but less than 360 degrees |

Null angle | 0 degrees |

Full rotation | 360 degrees |

Axiom | Statement that we accept without any proof. Without axioms there would be no starting point in theorems |

Theorem | Rule that has been proven by following a certain number of logical steps or by using a previous theorem or axiom that you already know |

Proof | Series of logical steps that we use to prove a theorem |

Corollary | Reverse of a theorem |

ImpliesH | Term we use in a proof when we can write down a fact that we have proven from our previous statements. |

Vertically opposite angles | Angles that have the same vertex and are directly opposite each other |

Transversal | Line that cuts two or more (usually parallel) lines |

Equilateral triangle | All sides and angles are equal |

Isosceles triangle | Two sides are the same length and two angles are the same size |

Scalene | 3 different lengths and 3 different angles |

Polygon | Closed shape (no gaps or openings) with straight sides. It has at least 3 sides |

Quadrilateral | Four sided polygon |

Parallelogram | Quadrilateral that has 2 pairs of parallel sides |

Congruent triangles | All corresponding sides and interior angles are equal in measure |

Pythagoras | Square on the hypotenuse is equal to the sum of the squares of the other 2 sides. |

Area of triangle | Half the base multiplied by the perpendicular height |

Area of parallelogram | Base multiplied by height |

Circle | Set of points in a plane that are all equidistant from a fixed point, its centre |

Radius | Line segment from the centre of the circle to any point on the circle |

Chord | Any segment that joins two points on a circle |

Diameter | Chord that passes through the centre of a circle. The diameter is twice the radius |

Circumference | Perimeter or length of the circle |

Tangent | A line which touches the circle at only one point |

Sector | Region of the circle enclosed by two radii and the arc between these radii |

Cyclic Quadrilateral | Measures of the opposite angles add up to 180 degrees |

Created by:
Holy Rosary College Mountbellew