quadrant One
of the four parts into which the coordinate plane is divided by the xaxis and yaxis.
quadrilateral A foursided polygon.
quadrillion A word name for
1,000,000,000,000,000.
quadrillionth A word name for 10^{15},
or .00000 00000 00001.
quart ( qt ) A unit of volume in the U.S.
system of measurement equal to 2 pints.
quintillion A word name for
1,000,000,000,000,000,000.
quintillionth A word name for 10^{18},
or .00000 00000 00000 001.
quotient The result of dividing one
number by another.

radius of a circle
( plural radii ) The distance from the center
of any point on the circle.
radius of a sphere The distance from the center to
any point on a sphere.
rate A quantity whose unit contains
the word " per " or " for each " or some synonym.
rate factor A 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.
rational number A
number that can be written as a simple fraction. A terminating or repeating decimal.
ray
A part of a line which begins at some point and goes on forever
in a particular direction.
real numbers A
number that can be written as a decimal.
reciprocal A
number which, when multiplied by a given number, yields the product 1. Also called multiplicative
inverse.
rectangle A
quadrilateral with four right angles.
rectangular array An arrangement of
objects into rows and columns.
rectangular solid A box.
reflecting line The
line over which a figure is reflected. Also called mirror.
reflection image
The image of a figure reflected over a line.
regular polygon
A convex polygon whose sides all have the same length and angles all have the same
measure.
Related Facts Property of Multiplication and Division If xy = P, then P/x = y and P/y = x.
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.
rhombus A quadrilateral with all
sides of the same length.
right angle An angle whose measure is
90°.
right triangle A triangle with a right
angle.
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 the exact value.
rounding up Making an estimate that
is bigger than the exact value.
row A horizontal line of objects in
a rectangular array. 