Word  Definition  Examples  

Data  Numbers collected for use in statistics and other forms of problem
solving. Data can be qualitative (yes/no, true/false) or quantitative(numbers). 
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 nonrepeating decimals. 
2.25 = 2 ¼ 

Deductive reasoning  A method of reasoning logically from given facts, rules, definitions, or properties to a
conclusion.
According to Wikipedia, "Deductive reasoning links premises with conclusions. If all premises are true, the terms are clear, and the rules of deductive logic are followed, then the conclusion reached is necessarily true." 
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  3x^{5}y^{2} 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  4x^{5} + 3x^{2}  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  4x^{5}y^{2} + 3x^{2}y^{2}  8 is 7th degree because the first term is degree 7 (5 + 2), the second term is degree 4 (2 + 2), and the number term is degree zero (no exponents). 

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). When you see something like ΔA , it can be read as change in A. 

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 on 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
For f(d) = 5t + 10, the value os f(d) depends on the value of t 

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.
In algebra, we find the slope of a line and the slope is a constant. The slope (derivative) of a curve is always changing because the curve is not straight. 

Diameter  In a circle, any segment that contains the center of the circle and has both
endpoints on the circle.
Two times the radius. 

Difference of two squares  A quadratic binomial of the form a^{2}  b^{2}, it
factors to (a + b)(a  b) 
Perfect square minus a perfect square  x^{2}  9 4x^{2}  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 
A line where one variable equals a constant times the other variable.  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. 

Discriminant  the term under the square root sign in the quadratic
formula: b^{2}  4ac


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
125 id divisable by 5 because the answer is exactly 25 
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 
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