Dictionary
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 random number generators
 A device used to produce a selection of numbers in a fair manner, in no particular
order and with no favor being given to any numbers. Examples include dice, spinners,
coins, and computer programs designed to randomly pick numbers (cf Random Number Generators Discussion).
 range
 The range of a set of numbers is the largest value in the set minus the smallest value
in the set. Note that the range is a single number, not many numbers.
 ratio
 A rational number of the form a/b where a is called the numerator and b is called the denominator.
 range of the function f
 The set of all the numbers f(x) for x in the domain of f.
 ray
 A straight line that begins at a point and continues outward in one direction (cfLines, Rays and Planes).
 real numbers
 Real numbers can be thought of as all the points falling along the number line in the coordinate plane (cf Two Variable Functions Discussion).
 rectangle
 A parallelogram with four
right angles (cf Rectangle
Discussion).
 recursion
 Given some starting information and a rule for how to use it to get new information, the rule is then repeated using the new information (cf Recursion Discussion).
 reflect
 In a tessellation, reflect means to repeat an image by flipping it across a line so it appears as it would in a mirror (cfTranslations, Reflections, and Rotations, Symmetry in Tessellations).
 regular fractals
 see fractal
(cf Plane Figure Fractals Discussion).
 regular polygon
 A polygon whose side lengths are all the same and whose interior angle measures are all the same (cf Polyhedra Discussion).
 relative frequency
 Relative frequency is the number of items of a certain type divided by the number of
all the numbers being considered.
 remainders
 After dividing one number by another, if any amount is left that does not divide evenly, that amount is called the remainder. For example, when 8 is divided by 3, three goes in to eight twice (making 6), and the remainder is 2. When dividing 9 by 3, there is no remainder, because 3 goes in to 9 exactly 3 times, with nothing left over (cf What are Remainders Discussion).
 rhombus
 A parallelogram with four congruent sides (cfParallelograms Discussion).
 right angle
 An angle of 90 degrees (cf
From Geometry to Probability Discussion, Rectangle Discussion).
 right triangle
 A triangle containing an angle of 90 degrees (cf
What is the Pythagorean Theorem).
 rotate
 To rotate an object in a tessellation means to repeat the object by spinning it on a point a certain angle (cfTranslations, Reflections, and Rotations, Symmetry in Tessellations).
 rule of probabilities multiplication for simultaneous
independent events
 When finding the probability of two independent events (two things happening where the outcomes are not affected by each other), multiply the probabilities of each event happening to get the probability of both
events happening. For example, to find the probability of getting "heads" and then
"tails" when flipping a coin twice, multiply the probability of getting heads once by
the probability of getting tails once
(cf Probability of Simultaneous Events Discussion).
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