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# Geometry Terms

### Geometry terms

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

Geometry | branch of mathematics that deals with points, lines, planes, and solids and examines their properties |

Point | Has no size, length, width, or height. It is represented by a dot and named by a capital letter. |

Line | Set of points that has infinite length and width but no height. We name this with a lower case letter or by any two points on the line. |

Plane | set of pints that has infinite length and width but no height. We name this with a capital letter. |

Space | Set of all point |

Collinear Points | points that lie on the same line |

noncollinear points | points that do not lie on the same line |

Coplanar Points | point that lie on the same plane |

Noncoplanar Points | points that do not lie on the same plane |

Segment | part of a line that consists of two points called endpoints and all points between them |

Ray | Is the part of a line that contains an endpoint and all points extending in the other direction |

congruent segments | segments that have the same length |

Bisectors of a segment | Line, ray segment, or plane that divides a segment into two congruent segments. |

Midpoint of a segment | a point that divides the segment into two congruent segments |

Acute angle | angle whose measure is between 0 and 90 degrees |

Right angle | angle whose measure is 90 degrees |

Obtuse angle | Angle whose measure is greater than 90 degrees but less than 180 degrees |

Straight angle | angle whose measure is 180 degrees |

Congruent angles | angles that have the same measure |

Angle bisector | ray that divides an angle into two congruent adjacent angles |

Triangle | The figure formed by three segments joining three noncollinear points. Each of the three points is a vertex of the triangle and the segments are sides. |

Acute triangle | triangle that has all acute angles |

Right triangle | Triangle with a right angle |

Obtuse triangle | Triangle with an obtuse angle |

Equilangular triangle | triangle with all angles congruent |

Scalene triangle | triangle with no sides congruent |

Isosceles triangle | Triangle with at least two sides congruent |

Equilateral triangle | Triangle with all sides congruent |

Adjacent angles | two coplanar angles with a common vertex and a common side between them |

Vertical angles | the non-adjacent angles formed by twointersecting lines |

Complementary angles | two angles whose sum is 90 degrees |

Supplementary angles | two angles whose sum is 180 degrees |

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

Parallel lines | two line are parallel if they are coplanar and do not intersect |

Skew lines | Are noncoplanar lines they will not intersect |

Polygon | Union of three or more coplanar segments that meet only at endpoints such that at most two segments meet at one endpoint and each segment meets exactly two other segments |

Regular polygon | polygon which is equilateral and equiangular |

Congruent Triangles | a triangle that has corresponding sides and corresponding angles congruent |

Median of a triangle | segment from the vertex of the triangle to the midpoint of the other side |

Altitude of a triangle | segment from the vertex of a triangle perpendicular to the line containing the opposite side |

Parallelogram | quadrilateral with both pairs of opposite sides parallel |

Rectangle | Parallelogram with a right angle |

Rhombus | Parallelogram with consecutive sides congruent |

Square | all sides congruent and all four right angles |

Trapezoid | quadrilateral with exactly one pair of opposite sides parallel |

Ratio | comparison of two numbers by division |

Proportion | equation that states that two ratios are equal |

Pythagorean Theorem | in a right triangle, the sum of the squares of the legs is equal to the square of the hypotenuse |

Circle | the set of points in a plane that are equidistant from a fixed point called the center |

Radius | Segment whose endpoints are the center of the circle and a point on the circle |

Chord | segment that connects two points on the circle |

Diameter | chord that passes through the center of the circle |

Secant | line that intersects a circle in two points |

Tangent | line in the plane of the circle the intersects the circle in one point |

Concentric Circles | two or more circles in the same plane with the same center |

Congruent Circles | circles that have congruent radii |

Sphere | set of points in space a given distance from a given point called the center |

Arc | consists of two points and the continuous part of a circle between them |

Semi-Circle | arc whose endpoints are the endpoints of a diameter |

Minor arc | arc whose measure is less than a semi-circle or 180 degrees |

major arc | arc whose measure is greater than a semi-circle of 180 degrees |

central angle of a circle | angle whose vertex is the center of the circle and whose rays are radii of the circle |

Congruent arcs | arcs with equal measure in the same circle or in congruent circles |

Inscribed angles | angle whose vertex is on the circle and whose sides are chords of the circle |

bases | congruent polygons lying in parallel planes |

Altitude | segment joining the two base planes and perpendicular to both |

Lateral faces | faces of a prism that are not its bases |

Lateral edges | intersection of adjacent lateral faces |

Lateral area | Sum of the area of its lateral faces |

Surface area | sum of the area of all faces |

Volume | number of cubic units contained in a solid |

Right prism | a prism whose lateral faces are rectangles |

oblique prism | a prism whose lateral faces are parallelograms |

cube | a prism where all sides are squares |

Triangular prism | a prism whose parallel faces are congruent triangles |

Cylinder | has two congruent circular bases in parallel planes |

Cone | has a vertex and a circular base |

Line of symmetry | divides a figure into two congruent halves that reflect each other |

Perimeter | the distance around the polygon |

Area | the number of square units needed to cover the figure |

Circumference | the distance around a circle |

conditional statement | a statement that can be written in if-then form |

Hypothesis | in a conditional statement, it is the statement that immediately follows the word if |

Conclusion | in a conditional statement, it is the statement that immediately follows the word then |

Converse | The statement formed by exchanging the hypothesis and the conclusion of a conditional statement |

Inverse | the statement formed by negating both the hypothesis and the conclusion of a conditional statement |

Contrapositive | the statement formed by negating both the hypothesis and conclusion of the converse of a conditional statement |

Biconditional | the conjunction of a conditional statement and its converse |

Proof | a logical argument in which each statement you make is supported by a statement that is accepted as true |

Postulate | a statement that describes a fundamental relationship between basic terms of geometry. These are accepted as true without proof. |

Theorem | A statement or conjecture that can be proven true by given, definitions, postulates, or already proven theorems. |

Two column proof | a formal proof that contains statements and reasons organized in two columns |

Paragraph proof | an informal proof written in the form of a paragraph that explains why a conjecture for a given situation is true |

Flow proof | a proof that organizes statements in logical order, starting with given statements |

Sine | for an acute angle of a right triangle, the ratio of the measure of the leg opposite the acute angle to the measure of the hypotenuse |

Cosine | for an acute angle of a right triangle, the ratio of the measure of the leg adjacent to the acute angle to the measure of the hypotenuse |

Tangent | for an acute angle of a right triangle, the ratio of the measure of the leg opposite the acute angle to the measure of the leg adjacent to the acute angle |

Created by:
karinmeuwissen