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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 |