Download CHAPTER ONE Geometry Glossary.

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CHAPTER ONE
Geometry Glossary.
TERM
DEFINITION
acute angle
An angle less than 90 degrees.
acute triangle
A triangle with three acute angles.
angle
Two rays that share a common endpoint provided that the two rays
are noncollinear. The common endpoint of the two rays is the vertex
of the angle. The two rays are the sides of the angle.
arc of a circle
Two points on the circle and the continuous part of the circle
between the two points.
bisects
To divide a figure into two congruent parts.
central angle
An angle with its vertex at the center of the circle, and sides passing
through the endpoints of an arc.
chord
Any line segment whose endpoints are on a circle.
circle
The set of all points in a plane at a given distance (radius) from a
given point (center) in the plane.
collinear
Two or more points that lie on the same line.
complementary angles
Two positive angles whose sum is 90 degrees.
concave
A polygon is concave if at least one diagonal is outside the polygon.
concentric circles
Two or more coplanar circles sharing the same center.
cone
A solid (3-dimensional) object that has a circular base and one
vertex. There are two types of cones: right cones and oblique cones.
The base of a cone is a circle and its interior. The radius of a cone is
the radius of the base. The vertex of a cone is point not in the same
plane as the base. The altitude of a cone is the perpendicular
segment from the vertex to the plane of the base. The height of a
cone is the length of the altitude. If the line segment connecting the
vertex of a cone with the center of its base is perpendicular to the
base, then it is a right cone.
congruent
Two geometric figures are congruent if and only if they are identical
in shape and size.
congruent circles
Two or more circles having radii with the same length.
congruent segments
Two segments are congruent segments if and only if they have the
same measure.
convex
A polygon is convex if no diagonal is outside the polygon.
coplanar
Two or more points that lie on the same plane.
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cylinder
A solid (three-dimensional object) with two circular bases and one
curved side. There are two types of cylinders: right cylinder and an
oblique cylinder. The bases of a cylinder are congruent circles. The
segment connecting the centers of the bases is called the axis of the
cylinder. (The axis of a right cylinder is perpendicular to the bases.)
The radius of the cylinder is the radius of a base. An altitude of a
cylinder is a perpendicular segment from the plane of one base to the
plane of the other. The height of a cylinder is the length of an
altitude.
decagon
A polygon with ten sides
definition
A statement that clarifies or explains the meaning of a word or a
phrase.
degrees
A measure of an angle.
diagonal
A diagonal of a polygon is a line segment that connects two
nonconsecutive vertices.
diameter
A line segment containing the center, with its endpoints on the circle
dodecagon
A polygon with twelve sides.
equiangular polygon
A polygon with angles having equal measure.
equilateral polygon
A polygon with sides having equal length.
equilateral triangle
A triangle with three sides of equal length.
hemisphere
Half a sphere
heptagon
A polygon with seven sides.
hexagon
A polygon with six sides.
isosceles triangle
A triangle with at least two sides of equal length. The angle between
the two sides of equal length is called the vertex angle. The side
opposite the vertex angle is called the base of the isosceles triangle.
The two angles opposite the two sides of equal length are called the
base angles of the isosceles triangle.
kite
A quadrilateral with exactly two pairs of distinct, congruent,
consecutive sides.
line
An undefined term. A straight arrangement of points. There are
infinitely many points in a line. A line has infinite length but no
thickness and extends forever in two directions.
linear pair of angles
Two angles sharing a vertex and a common side and their noncommon sides form a line.
line segment
Two points and all the points between them that lie on the line
containing the two points. The two points are called the endpoints of
the line segment.
major arc
An arc of a circle that is larger than a semicircle.
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midpoint
The point on the segment that is the same distance from both
endpoints.
minor arc
An arc of a circle that is smaller than a semicircle.
nonagon
A polygon with nine sides
octagon
A polygon with eight sides.
obtuse angle
An angle whose measure is more than 90 degrees, but less than 180
degrees.
obtuse triangle
A triangle with one obtuse angle
parallelogram
Any quadrilateral in which both pairs of opposite sides are parallel.
parallel lines
Two coplanar lines that lie in the same plane and never intersect.
pentagon
A polygon with five sides.
perpendicular
Lines that intersect to form right angles.
plane
An undefined term. A plane has length and width, but no thickness. It
is a flat surface that extends forever.
point
An undefined term. The basic unit of geometry. It has no size, is
infinitely small, and has only location.
polygon
A closed figure in a plane, formed by connecting line segments
endpoint to endpoint with each segment intersecting exactly two
others.
prism
A polyhedron with two faces (bases) that are congruent and parallel
polygons and whose other faces (lateral faces) are parallelograms
formed by segments (lateral edges) connecting the corresponding
vertices of the bases.
protractor
A geometry tool used to measure an angle.
pyramid
A polyhedron with one face (base) that is a polygon and whose other
faces (lateral faces) are triangles formed by segments (lateral edges)
that connect the vertices of the base to a point (vertex) not on the
base. The altitude of a pyramid is the perpendicular segment from the
vertex to the plane of the base, and the height of a pyramid is the
length of the altitude.
quadrilateral
A polygon with four sides.
radius
A segment from the center to a point on the edge of the circle.
ray
Ray AB is the part of line AB that contains point A and all the points
on line AB that are on the same side of A as B. Point A is the
endpoint of ray AB.
rectangle
Any equiangular parallelogram.
regular polygon
A polygon that is both equilateral and equiangular.
rhombus
Any equilateral parallelogram.
right angle
A 90 degree angle
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right triangle
A triangle with one right angle.
scalene triangle
A triangle with no sides of equal length.
semicircle
An arc of a circle whose endpoints are the endpoints of a diameter.
sphere
The set of all points in space at a given distance from a given point.
The given distance is called the radius and the given point is the
center.
square
An equiangular rhombus or an equilateral rectangle.
straight angle
A 180 degree angle
supplementary angles
Two positive angles whose sum is 180 degrees.
tangent
A line that touches a circle at exactly one point.
trapezoid
A quadrilateral with exactly one pair of parallel sides. The parallel
sides are called bases. A pair of angles that share a base as common
side are called a pair of base angles.
triangle
A polygon with three sides
undecagon
A polygon with eleven sides
vertical angles
Angles formed by two intersecting lines; they share a common vertex
but not a common side.
vertex
(1) The common endpoint for two rays that determine an angle; (2)
an endpoint of a side of a polygon.
"My subjects are often playful...It is, for example, a pleasure to deliberately mix together
objects of two and of three dimensions, surface and spatial relationships, and to make fun of
gravity."
M. C. ESCHER (1898-1972