radius of a circle or sphere A segment connecting the center of a circle or a sphere with a point on that circle or sphere, also, the length of that segment. Plural is radii.
rate A quantity whose unit contains the word " per " or " for each " or some synonym.
rate used in multiplication .
Rate Model for Division If a and b are quantities with different units, then a/b is the amount of quantity a per quantity b.
Rate Factor Model for Multiplication When a rate is multiplied by another quantity, the unit of the product is the ( product ) of units multiplied like fractions. The product has meaning whenever its units have meaning.
rate unit The unit of measurement in a rate.
ratio The quotient of two quantities with the same units.
Ratio Comparison Model for Division If a and b are quantities with the same units, then a/b compares a to b.
ratio of similitude In similar figures, the ratio of a distance or length in an image to the corresponding distance or length in a preimage.
rational number A number that can be written as a simple fraction. These numbers can also be written as terminating or repeating decimals.
A part of a line which begins at some point and goes on forever in a particular
direction. The ray with endpoint A containing B is denoted
real numbers A number that can be written as a decimal. The set of Real numbers is made up of all rational numbers as well as all irrational numbers.
reciprocal A number which, when multiplied by a given number, yields the product 1. Also called multiplicative inverse. An example of this is the numbers 2 and 1/2. When multiplied, they yield 2/2, which equals 1.
A quadrilateral with four right angles.
arrangement of objects into rows and columns.
A box. The union of a box and its interior.
line over which a preimage is reflected. Also called mirror line
or line of reflection.
reflecting plane The plane over which a preimage is reflected. Also called mirror.
reflection A transformation in which each point is mapped onto its reflection image over a line or plane.
reflection image The image of a figure reflected over a line.
region The union of a polygon or circle with its interior is known as a region.
A convex polygon whose sides all have the same length and angles all have
the same measure.
regular polyhedron A convex polyhedron whose faces are all congruent regular polygons and the same number of edges intersect at each of its vertices. There are only five of these that can be constructed out of a single polygon shape. They are:
A right prism whose base is a regular polygon.
A right pyramid whose base is a regular polygon and whose lateral faces
are congruent isosceles triangles.
Facts Property of Multiplication and Division
If xy = P, then P/x = y and P/y = x. Or a numerical
Repeated Addition Model for Multiplication If n is a positive integer, then nx = x + x + . . . + x. ( n addends)
repetend The digits which repeat forever in an infinitely repeating decimal.
revolution A turn of 360°. Also called full turn.
A quadrilateral with all sides of the same length.
angle whose measure is 90°. A right angle will always be drawn with a
small square at its vertex. This removes all doubt that it is a 90 degree
angle. If you don't see the square you cannot assume that it is
a right angle.
method for finding the center of a circle that involves constructing two
inscribed right triangles. The intersection of their hypotenuses is the
A cone whose axis is perpendicular to the plane of the circular base.
A cylinder formed when the two circular bases are directly across from
each other. The walls of a right cylinder are perpendicular to both bases.
A right prism is formed when two polygonal bases are placed right across
from each other. The walls of a right prism are perpendicular to both
A pyramid whose base is a regular polygon and in which the segment connecting
its vertex to the center of its base is perpendicular to the plane of
triangle with a right angle.
A transformation in which every point of the preimage is rotated by a
given angle about a point (in two dimensions) or a line (in three dimensions).
A figure which when rotated less than 360 degrees will lie on top of itself.
rounding down Making an estimate that is smaller than the exact value.
rounding to the nearest Making an estimate to a particular decimal place by either rounding up or rounding down depending on which estimate is closest to the exact value.
rounding up Making an estimate that is bigger than the exact value.
round-robin tournament A tournament in which each competitor plays each other exactly once.
row A horizontal line of objects in a rectangular array.
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