# Math Vocabulary - D

Word Definition Examples
D Data Numbers collected for use in statistics and other forms of problem solving. Data can be in lists, tables, graphs, charts, and many other ways.
Decimals A number written with place value instead of fractions or mixed numbers. Also used to approximate irrational numbers. See repeating decimals, truncated decimals , and non-repeating decimals.

2.25 = 2 Ľ
decimal   fraction

Deductive reasoning A method of reasoning logically from given facts, rules, definitions, or properties to a conclusion. All oranges are fruits
All fruits grow on trees
Therefore, all oranges grow on trees
Degree of a monomial The sum of the exponents of all its variables 7x5y2 is 5 + 2 or 7th degree
Degree of a polynomial (single varable) For a polynomial with only one variable, the highest degree of any of its terms The biggest positive exponent 7x5 + 3x2 - 8 is fifth degree
Degree of a polynomial (multiple varables) For a polynomial with more than one variable, the highest degree of any of its terms 7x5y2 + 3x2y2 - 8
is 7th degree because the first term is degree 7, the second term is degree 4, and the number term is degree zero.
Delta Δ δ Greek letter frequently used to represent variables that change. Capital Δ usually represents a larger change (like slope) and small δ is a small change (used in physics and calculus).
Dependent events In probability, when the outcome of one event affects the outcome of a second event, the events are dependent The probability of getting 2 heads in a row when you flip coins depends on if you get a head the first toss.
Dependent variable A variable that relies on the value of another variable for y = x + 2, the value of y depends on the value of x
Derivative In Calculus, the formula for slope of a graph at any point on the graph. The process of finding the derivative is called differentiation
Diameter In a circle, any segment that contains the center of the circle and has both endpoints on the circle.
Difference of two squares A quadratic binomial of the form a2 - b2, it factors to
(a + b)(a - b)
Perfect square minus a perfect square x2 - 9
4x2 - 25
Dilation A transformation in which a figure is made larger or smaller, but not moved. Direct variation A linear function of the form y = kx,
where k ≠ 0
A straight line that passes through (0,0) with slope k y = 5x
y = -2x
Discrete Data Involves a count of data items Things that can be counted heart beats in a minute or
daily temperature at noon
Discontinuous Function A graph of a function that has jumps, holes or breaks. It cannot be graphed without lifting your pencil.
• if the discriminant is positive the equation has 2 real solutions
• if the discriminant = zero there is 1 real solution
• if the discriminant is negative there are 2 imaginary solutions
Distance Formula Using the Phythagorean Theorem to find the distance between two points on a coordinant grid) Distributive property For all real numbers a, b, and c:
a(b + c) = ab + ac
a(b - c) = ab - ac
Multiply everything inside the parenthesis by the thing in front of the parentheses 5(x + 2) = 5x + 10
4(x - 2) = 4x - 8
Divisible a number that can be divided by a whole number with no remainder See Divisibility Rules
Domain The set of all possible input values - the independent variable in a function. For functions in x and y, the possible x values are the domain. For y = 2x + 6, the domain is all real numbers

For y = 7/x, the domain is all real numbers except 0 because you can't divide by zero

Word Definition Examples
E    Element
1. Each object or number in a set
2. Each entry in a matrix

Elimination Using addition or subtraction to eliminate one variable when solving a system of equations.
End behavior The way a graph of an equation behaves at the far left and right ends as the input variable goes to positive or negative infinity +
Epsilon Ε ε Greek letter sometimes used in math problems
Equation Two expressions that are equal. Uses the = sign to show the relationship that two things are equal to each other.
Each side of the equation is an expression.
x + 2 = 7

4x2 + 2x = 7

Equiangular polygon A polygon where all the angles are congruent

All angles equal

Equiangular triangle A triangle where all the angles are congruent

All angles equal

Equilateral polygon A polygon where all the sides are congruent All sides equal
Equilateral triangle A triangle where all the sides are congruent

All sides equal

Euler Line In geometry, the centroid, circumcenter and orthocenter of any triangle always lie on a straight line, called the Euler line. Click here to see an animated example of the Euler line.
Even function A function graph whose axis of symmetry is the y-axis. f(x) = f(-x) y = 5x2 + 2
Even number Any number that can be divided by 2 with no remainder. In Algebra, 2n can represent any even number.
Event In probability, any group of outcomes The possible results When rolling one dice, the outcomes are 1, 2, 3, 4, 5, or 6
Exact number Am number that is the result of counting or the results from a theoretical calculation. Measurements are not exact numbers.
Experimental data In statistics, data that collected from an experiment set up specifically to answer a question.
Experimental probability In probability, the ratio of the number of times an event happens to the number of times the experiment is done Results from doing an experiment P(event) = times it happened ÷ times you tried
Exponent A raised number that represents repeated multiplication of a factor 34 = 3 • 3 • 3 • 3
Exponential decay An equation used to calculate how things get smaller over time - used for radioative decay and age dating. y = C(1 - r)t
where y is the final amount, C is the original amount, r is the rate of change, and t is time.
Exponential function An equation of the form y = bx where there is a variable as an exponent. Exponential functions are the inverse of logarithms Exponential growth An equation used to calculate how things increase over time - used for growth of bacteria and other populations. y = C(1 + r)t
where y is the final amount, C is the original amount, r is the rate of change, and t is time.
Expression Any combination of values and operations (no = sign) 4x2 + 2x
Exterior angle In a polygon, the angle formed by a side and an extension of a side. Extraneous Solution A number that comes when you solve an equation, but it doesn't work in the original equation. Frequently occurs in equations that have a variable under a square root sign.
Word Definition Examples
F    Factoring Breaking a polynomial equation down into the product of several factors
 y = x2 - 3x + 2 Original problem y = (x - 2)(x - 1) Factored form
Factorial ! n! is the product of all the whole numbers from n down to 1 - used in probability 3! =  3• 2 • 1 = 6
4! = 4 •
3• 2 • 1 = 24
Factors Whole numbers that are multiplied together to equal  another number. See Divisibility Rules 2 and 5 are the factors of 10 because 10 = 2 • 5
Factored Form A polynomial written as the product of polynomials of lower degree y = (x + 4)(x - 3) is the factored form of
y= x2 + x - 12
Favorable outcome In a probability experiment, the possible results you want to happen When flipping coins and you call heads, a favorable outcome is you getting heads.
FOIL method When multiplying two binomials, use the Distributive property repeatedly.
F - first terms in each parentheses
O - outside terms in each parentheses
I - inside terms in each parentheses
L - last terms in each parentheses Fraction A ratio of two numbers representing part of a whole. A fraction is a real number. In Algebra, a fraction bar means to divide. ˝ means one half

it also means 1 divided by 2

Frequency The number of cycles per unit of time or the reciprocal of the period of the function. Foundation drawing Drawing that shows the base of an object (its foundation) and the height of each part.
Function A relation that assigns exactly one value of the dependent variable to each value of the independent variable Rule that matches one input to only one answer y = x + 5 is a function
if you pick x = 3 you get one answer, y = 8
Function notation A function written using the symbol f(x) in place of y Another name for a function - a more formal name. Read it as "f of x" f(x) = 2x + 3
y = 2x + 3
Future value In investment problems with interest, the future value is the value of the investment after interest has been earned.
Comments, questions, or you just need some help? Send an e-mail to Mrs. Shearer Last Updated: 06/14/2014