quadrant  One of the four parts into which the coordinate plane is divided by the x-axis and y-axis.

quadrilateral A four-sided 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.