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# Geometry To Know

### Study the major geometry terms you need to know.

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

a one dimensional figure that extends forever in both directions | line |

part of a line, with two endpoints | segment |

a point at the end of a line segment or ray | endpoint |

a part of a line that has one endpoint and extends forever in the other direction | ray |

to cross through the same point | intersect |

two lines that cross (intersect) at right angles | perpendicular |

two lines, segments, or rays that do not cross, no matter how far they extend | parallel |

two rays with the same endpoint | angle |

each of the rays forming an angle | side |

the common endpoint of two rays forming an angle | vertex |

a unit of angle measure ( 1/360 of a complete circle), represented with (°) | degree |

a tool that measures angles | protractor |

an angle that measures 90°, it forms a perfect corner | right angle |

an angle smaller than a right angle | acute angle |

an angle greater than a right angle but smaller than a straight angle (between 90° and 180°) | obtuse angle |

an angle formed by two rays pointing in opposite directions (180° angle) | straight angle |

two angles whose measures add up to 90°; they make a Corner | complimentary angles |

two angles whose measures add up to 180°; they make a Straight line | supplementary angles |

angles with the exact same measure | congruent angles |

a closed figure made of line segments | polygon |

a closed figure made from three line segments | triangle |

The sum of the angles in a triangle must equal | 180 degrees |

a triangle with three acute angles (all angles < 90°) | acute triangle |

a triangle with an obtuse angle (one angle > 90°) | obtuse angle |

a triangle with a right angle (one angle=90°) | right angle |

the longest side of a right triangle (the side opposite the right angle) | hypotenuse |

either of the two sides in a right triangle that form the right angle | leg (of a right triangle) |

a triangle with three sides of the same length | equilateral triangle |

a triangle with at least two sides of the same length | isosceles triangle |

a triangle with no sides of equal length | scalene triangle |

a polygon whose sides and angles have equal measures | regular polygon |

a polygon that does NOT have all sides and angles equal | irregular polygon |

two polygons with the exact same shape but of different size | congruent polygons |

a closed figure made from 4 line segments | quadrilateral |

a closed figure made from 5 line segments | pentagon |

a closed figure made from 6 line segments | hexagon |

a closed figure made from 7 line segments | heptagon |

a closed figure made from 8 line segments | octagon |

a closed figure made from 9 line segments | nonagon |

a closed figure made from 10 line segments | decagon |

The sum of the angles in a quadrilateral must equal | 360 degrees |

a quadrilateral with exactly two sides parallel | trapezoid |

a quadrilateral whose opposite sides are parallel and equal | parallelogram |

a parallelogram with all sides the same length (irregular quadrilateral, parallelogram) | rhombus |

a parallelogram with opposite sides the same length and all angles measuring 90° (irregular quadrilateral, parallelogram) | rectangle |

a parallelogram with all sides the same length and all angles measuring 90°(regular quadrilateral, parallelogram, rhombus) | square |

a set of points that are a given distance from a center point | circle |

the distance around the outside of a circle | circumference |

a line segment from the center of the circle to any point on the circle | radius |

a line segment whose endpoints are on a circle | chord |

a line segment connecting two points on a circle and passing through the center (a special kind of chord) | diameter |

a flat surface that extends forever in all directions | plane |

a location on a plane with no length, no width, and no depth | point |

a set of lines used to locate points on a plane | coordinate plane |

vertical axis (up & down) | y-axis |

horizontal axis (across) | x-axis |

always read the ____-axis first | X |

a pair of numbers used to locate a point on a coordinate plane (x,y) | ordered pair(coordinates) |

Created by:
mlasalle