Math Glossary Letter R
radian
noun
a unit of plane angular measurement that is equal to the angle at the center of a circle subtended by an arc whose length equals the radius or approximately 180°/π ~ 57.3 degrees.
radical
noun
The √ symbol that is used to denote square root or nth roots

radical expressions
noun
an nth root of a number x is a number r which, when raised to the power n, yields x

n√x
radius
noun
Distance from the center of a circle to the edge

C/2π
random number
noun
a number chosen by chance
random sampling
verb
a part of the sampling technique in which each sample has an equal probability of being chosen
random test
noun
selecting people for a test arbitrarily
random variable
noun
a variable whose value is unknown or a function that assigns values to each of an experiments outcomes
range
noun
Difference between the largest and smallest values in a number set
rank
noun
the data transformation in which numerical or ordinal values are replaced by their rank when the data are sorted.
rankine
noun
an absolute scale of thermodynamic temperature named after the University of Glasgow engineer and physicist Macquorn Rankine
rate
noun
the ratio between two related quantities in different units. A measure, quantity, or frequency.
rate of return
noun
the gain or loss of an investment over a specified period of time, expressed as a percentage of the investments cost.
ratio
noun
indicates how many times one number contains another
rational exponents
noun
exponents that can be expressed in the form of p/q, where q ≠ 0.
rational expressions
noun
Quotient of two polynomials

P(x)/Q(x)
rational number
noun
a number that can be expressed as the quotient or fraction p/q of two integers
rational root theorem
noun
used to find the rational solutions of a polynomial equation
rational zero theorem
noun
used to find the rational roots of a polynomial function
ray
noun
a part of a line that has a fixed starting point but no endpoint
real number
noun
a value of a continuous quantity that can represent a distance along a line.
reaumur
noun
elating to or conforming to a thermometric scale on which the boiling point of water is at 80° above the zero of the scale and the freezing point is at zero.
rebound ratio
noun
how high the ball bounces after a static number of bounces,

Downward Distance at time n = h(1 - rr%n)/(1 - rr%)
receivable
noun
the money a company's customers owe for goods or services they have received but not yet paid for.
receivables ratio
noun
measures the efficiency with which a company is able to collect on its receivables or the credit it extends to customers
reciprocal
noun
a number which when multiplied by x yields the multiplicative identity, 1
rectangle
noun
a quadrilateral with four right angles
rectangle word problem
noun
a mathematical problem expressed entirely in words involving rectangle area or perimeter typically used as an educational tool
rectangular
noun
A 4-sided flat shape with straight sides where all interior angles are right angles (90°).
rectangular form
noun
an equation composed of variables like x and y which can be graphed on a regular Cartesian plane.
rectangular solid
noun
a 3 dimensional object with six sides, all of which are rectangles
recursive algorithm
noun
an algorithm which calls itself with smaller (or simpler) input values, and which obtains the result for the current input by applying simple operations to the returned value for the smaller (or simpler) input.
reduced digit sum
noun
sum all the digits until the sum < 10
reduced row echelon
noun
a matrix if and only if it is in row echelon form, all its pivots are equal to 1 and the pivots are the only non-zero entries of the basic columns.
reducing fractions
noun
divide both the numerator and denominator by the GCF
reference angle
noun
the smallest possible angle made by the terminal side of the given angle with the x-axis.
reflect
noun
a flip creating a mirror image of the shape
reflexive property
noun
a number is always equal to itself

a = a
regression
noun
a set of statistical processes for estimating the relationships between a dependent variable and one or more independent variables.
regrouping
verb
make groups of ten when performing operations such as addition or subtraction.
relative coordinates
noun
coordinates specified in relation to previous coordinates
relative error
noun
the ratio of the absolute error of a measurement to the measurement being taken.
reliability
noun
the overall consistency of a measure
remainder
noun
The portion of a division operation leftover after dividing two integers
repeating decimal
noun
a decimal fraction in which a figure or group of figures is repeated indefinitely, as in 0.1111
repunit numbers
noun
numbers that only contain 1s for digits
reserve
noun
To save something or set it aside for future use.
reserve ratio
noun
the portion of reservable liabilities that commercial banks must hold onto, rather than lend out or invest
resistance
noun
the property of any object or substance of resisting or opposing the flow of an electrical current.

R = V/I
resistor
noun
a passive two-terminal electrical component that implements electrical resistance as a circuit element
resistor color codes
noun
colour code used to denote the tolerance rating of a resistor is given
return
noun
a performance measure used to evaluate the efficiency of an investment or compare the efficiency of several investments.
revenue
noun
the money generated from normal business operations, calculated as the average sales price times the number of units sold
revolution
noun
A 360° angle, a full rotation, a complete turn so it points back the same way.
rgb
noun
an additive color model in which the red, green, and blue primary colors of light are added together in various ways to reproduce a broad array of colors.
rho
noun
A letter of the greek alphabet used for math notation.

Ρ  ρ
rhombus
noun
a quadrilateral with both pairs of opposite sides parallel and all sides the same length
right angle
noun
angle measuring 90 degrees
right triangle
noun
triangle in which one angle is a right angle
rise over run
noun
another way to say slope
risk
noun
expose (someone or something valued) to danger, harm, or loss.
risk free rate
noun
the rate of return offered by an investment that carries zero risk
roman numeral
noun
any of the letters representing numbers in the Roman numerical system: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1,000. In this system, a letter placed after another of greater value adds (thus XVI or xvi is 16), whereas a letter placed before another of greater value subtracts (thus XC or xc is 90).
root
noun
Value where a function equals zero
root mean square
noun
the square root of the mean square of the set
roster notation
noun
a simple mathematical representation of the set in mathematical form
rot13
noun
simple letter substitution cipher that replaces a letter with the 13th letter after it in the alphabet.
rotate
noun
a motion of a certain space that preserves at least one point.
roulette
noun
a gambling game in which a ball is dropped onto a revolving wheel ( roulette wheel ) with numbered compartments, the players betting on the number at which the ball will come to rest.
rounding
verb
replacing a number with an approximate value that has a shorter, simpler, or more explicit representation
royal flush
noun
a straight flush including ace, king, queen, jack, and ten all in the same suit, which is the hand of the highest possible value when wild cards are not in use.
ruffinis rule
noun
an efficient method of dividing a polynomial by a linear factor, with or without a remainder.
rule of 72
noun
a simplified formula that calculates how long it will take for an investment to double in value, based on its rate of return.

t ~ 72/i
rule of product
noun
If there are n(A) ways to do A and n(B) ways to do B, then the number of ways to do A and B is n(A) n(B)

n(A) n(B)
rule of succession
noun
a formula introduced in the 18th century by Pierre-Simon Laplace in the course of treating the sunrise problem

(s + 1)/(n + 2)
run length encoding
verb
a form of lossless compression