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# Arlene's Geometry

### Arlene A's Class - Terms from Geometry in our Math block

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

point | has no length, width or thickness |

line | has length but no width or thickness |

plane | has length and width but no thickness |

straight line segment | the part of a straight line between two of its points |

midpoint | if a line is divided into two equal parts, this is the point of division |

congruent segments | two segments having the same length are said to be this |

circle | the set of all points in a plane that are the same distance from a point |

circumference | distance around a circle |

radius | a segment that joins the center of a circle to a point on the circle |

central angle | an angle formed by two radii |

chord | a segment joing any two points on a circle |

diameter | a chord through the center of a circle |

arc | a continuous part of the circle |

semicircle | an arc measuring one half the circumference of a circle |

congruent circles | circles having congruent radii are said to be this |

angle | the figure formed by two rays with a common end point |

acute angle | an angle whose measure is less than 90 degrees is said to be an |

right angle | an angle that measures 90 degrees is said to be a |

obtuse angle | an angle that measures more than 90 degrees and less than 180 degrees is said to be an |

straight angle | an angle that measures 180 degrees is said to be a |

reflex angle | an angle whos measure is more thatn 180 degrees and less than 360 degrees is said to be a |

congruent angles | two angles that have the same number of degrees are said to be |

angle bisector | a line that divides an angle into two equal parts |

perpendicular | lines, rays or segments that meet at right angles are said to be |

perpendicular bisector | a segment that is bisects and is perpendicular to another segment |

polygon | a closed plane figure bounded by straight line segments at the sides |

pentagon | a polygon with 5 sides |

triangle | a polygon having three sides |

vertex | the point at which two of sides of a polygon meet |

scalene | a triangle that has no congruent sides |

isosceles | a triangle that has at last two congruent sides |

legs | the equal sides of an isosceles triangle |

base angles | the angles on either side of the base of an isosceles triangle |

base | the side of an isosceles triangle that are not the legs |

equilateral | a triangle that has three congruent sides |

right triangle | a triangle that has a right angle |

obtuse triangle | a triangle that has an obtuse angle |

acute triangle | a triangle that has three acute angles |

angle bisector of a triangle's angle | a segment or ray that bisects the angle of triangle and extends to the opposite side |

median of a triangle | a segment from a vertex to the midpoint of the opposite side |

perpendicular bisector of a triangle's side | a line that bisects and is perpendicular to a side of a triangle |

altitude of a triangle | a segment from the vertex of a triangle to the opposite side |

outside the triangle | in an obtuse triangle, an altitude drawn on either side of an obtuse angle falls here |

adjacent angles | two angles which have the same vertex and a common side |

vertical angles | two nonadjacent angles formed by two intersecting lines |

complementary angles | two angles whose measures add to 90 degrees |

supplementary angles | two angles whose measures add to 180 degrees |

transitive postulate | things equal to the same things are equal to each other |

subtitution postulate | a quantity may be substituted for its equal in any expression or equation |

partition postulate | the whole equals the sum of its parts |

reflexive or identity postulate | any quantity equals itself |

addition postulate | if equals are added to equals, the sums are equal |

subtraction postulate | if equals are subtracted from equals, the differences are equal |

multiplication postulate | if equals are multiplied by equals, the products are equal |

division postulate | if equals are divided by equals, the quotients are equal |

powers postulate | like powers of equals are equal |

postulate 10 | like roots of equals are equal |

one | the number of straight lines that can be drawn through any two points |

theorem | a statement, which proved, can be used to prove other statements |

CPCTC | congruent parts of congruent triangles are congruent |

SAS | a way of proving two triangles are congruent when they have two sides and the included angle congruent to each other |

orthocenter | the intersection point of a triangles altitudes |

incenter | the angle bisectors of a triangle meet at this point |

circumcenter | the perpendicular bisectors of the triangle meet at this point |

centroid | the intersection point of the three medians in a triangle |

Created by:
cathyhk