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# Geometry Terms

### Geometry terms

TermDefinition
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