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# 8th Grade Mathematics - Important Vocabulary Words

The mathematical vocabulary terms below can be found in the Mathworks Math Explorations textbooks.

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Absolute Value:

1. A number’s distance from zero.
2. For any x, is defined as follows: |x| =  −x, if x < 0; x, if x ≥ 0.

Acute Angle: An angle whose measure is greater than 0 and less than 90 degrees.

Acute Triangle: A triangle in which all three angles are acute angles.

Algebraic Expression: An expression that includes one or more variables and may also include symbols indicating an operation or a relationship.

Area Model: A mathematical model based on the area of a rectangle, used to represent multiplication or to represent fractional parts of a whole.

Axis of Symmetry: The vertical line x = − b/(2a) for the parabola given by f(x) = ax² + bx + c or the vertical line x =  h when written f(x) = a(x − h)² + k.

Base:

1. For any number x raised to the nth power, written as x^n, x is called the base of the expression.
2. In geometry any side of a triangle may be called the base.

Cartesian Plane: See: Coordinate Plane

Coefficient: In the product of a constant and a variable the constant is the numerical coefficient of the variable and is frequently referred to simply as the coefficient.

Common Factor: A factor that appears in two or more terms.

Compound Interest: Interest paid on previous interest which was added to the principal.

Consistent system: See: System of Equations

Convex Polygon: A plane, closed, figure formed by three or more line segments intersecting only at end points and each interior angle being less than 180 degrees.

Coordinate(s): A number assigned to each point on the number line which shows its position or location on the line. In a coordinate plane the ordered pair, (x, y), assigned to each point of the plane showing its position in relation to the x-axis and y-axis.

Coordinate Plane: A plane that consists of a horizontal and vertical number line, intersecting at right angles at their origins. The number lines, called axes, divide the plane into four quadrants. The quadrants are numbered I, II, III, and IV beginning in the upper right quadrant and moving counterclockwise.

Counterclockwise: A circular movement opposite to the direction of the movement of the hands of a clock.
Counting numbers: The counting numbers are the numbers in the following never-ending sequence: 1, 2, 3, 4, 5, 6, 7, . . . We can also write this as +1,+2,+3,+4,+5,+6,+7, . . .. These numbers are also called the positive integers or natural numbers.

Cube: The third power of a number.

Cube Root: For real number x and y, y is the cube root of x, (written √3 x ), if y³ = x.

Data Set: A collection of information, frequently in the form of numbers.

Degree: The degree of a term is the sum of the exponents of the variables. The degree of a polynomial is the highest degree of any of its terms. If it contains no variables its degree is 0 if it is non-zero, and undefined if the polynomial is zero.

Dependent System: See: System of Equations

Dependent Variable: The variable in a function representing the elements of the range; the output values.

Direct Variation: For real variables x and y, y varies directly with x if y = Kx or yx = K for a constant K, K  0. K is called the constant of proportionality.

Discriminant: The expression b² −4ac that appears under the radical sign in the Quadratic Formula.

Domain: The set of input values in a function.

Elements: Members of a set.

Equation: A math sentence using the equal sign to state that two expressions represent the same number.

Equivalent Equations: Two equations are equivalent if they have the same solution or solution set.

Equivalent Inequalities: Two inequalities are equivalent if they have the same solution set.

Equivalent Expression: Expressions that have the same numerical value for given values of the variables.

Exponent: Suppose that n is a whole number. Then, for any number x, the nth power of x, or x to the nth power, is the product of n factors of the number x. This number is usually written x^n. The number x is usually called the base of the expression x^n, and n is called the exponent.

Exponential Function: For numbers a, k and b  0, the function f(t) = (ab)^ t/k is called an exponential function. The number a = f(0) is the initial value, b is the base and k is a constant related to growth rate or period.

Exponential Growth/Decay: Also see Exponential Function.
For a > 0 and b > 1 the function denotes growth; for a > 0 and 0 < b < 1 the function denotes decay.

Exponential Notation: A notation that expresses a number in terms of a base and an exponent.

Extraneous Solutions: Apparent solutions which do not satisfy the given equation; usually introduced by raising to a power or multiplying by the variable in obtaining the solution.

Factor:

1. For integers a, b and c, a and b are factors of c if c = ab. Similarly f(x) and g(x) are factors of p(x) if p(x) = f(x) · g(x).
2. Factor is also used as an instruction or command to express a given integer or polynomial as a product.

Formula: An equation showing the relationship between two or more quantities represented by variables.

Function: A function is a rule which assigns to each member of a set of inputs, called the domain, a member of a set of outputs, called the range.

Function Notation: f(x), read ”f of x”, forming one side of an equation and used to indicate the value of the function when the input is x. Also see Function.

Graph of a Function: The pictorial representation of a function by plotting all of its input-output pairs on a coordinate system.

Height: In a triangle it is the segment from a vertex perpendicular to the selected base. Also used to refer to the length of that segment.

Horizontal Axis: See: Coordinate Plane

Hypotenuse: The side opposite the right angle in a right triangle.

Inconsistent system: See: System of Equations

Independent system: See: System of Equations

Independent Variable: The variable in a function representing the elements of the domain; the input values.

Inequality: A statement that two expressions represent different values. There are various forms.

Strict Inequalities: Statements such as “x is less than y”, (x < y ), and “x is greater than y”, (x > y ).

Weak inequalities: Statements such as “x is less than or equal to y”, (x ≤ y ), and “x is greater than or equal to
y”, ( x ≥ y).

General inequality: The statement ”x is not equal to y”, (x  y ).

Input Values: The values of the domain of a function.

Integers: The collection of integers is composed of the negative integers, zero and the positive integers: . . . ,−4,−3,−2,−1, 0, 1, 2, 3, 4, . . ..

Intersection of Sets: A set whose elements are all the elements that the given sets have in common.

Inverse Variation: For real variables x and y, y varies inversely with x if yx = K or y = Kx and K is a non-zero constant.

Irrational Number: A decimal number that neither repeats nor terminates. A number that can not be expressed as an integer divided by an integer.

Joint Variation: For variables x, y and z, z varies jointly with x and y if z = Kxy and K is a non-zero constant.

Legs: The two sides of a right triangle that form the right angle.

Less Than, Greater Than: The statement that the number a is less than the number b, written a < b means that there is a positive number x such that b = a + x. The number x must be b− a. If a is less than b, then b is greater than a, written b > a.

Like Terms: Algebraic terms that contain the same variables and for each variable the power is the same.

Linear Model for Multiplication: Skip counting on a number line.

Multiple: An integer or polynomial is said to be a multiple of any of its factors.

Multiplicative Identity: For each n, n · 1 = n and 1 is called the identity element for multiplication.

Multiplicative Inverse: The number x is called the multiplicative inverse or reciprocal of n, n  0 , if n · x = 1. This may also be written as n · 1/n = 1.

Natural Numbers: See: Counting Numbers

Negative 1 Power: If x is non-zero, x^−1 is the number 1/x

Non-negative Numbers: Numbers greater than or equal to zero.

Obtuse Angle: An angle whose measure is greater than 90 and less than 180 degrees.

Obtuse Triangle: A triangle that has one obtuse angle.

Ordered pair: A pair of numbers that represent the coordinates of a point in the coordinate plane with the first number measured along the horizontal scale and the second along the vertical scale.

Origin: The point with coordinate 0 on a number line; the point with coordinates (0, 0) in the coordinate plane.

Output Values: The set of results obtained by applying a function rule to a set of input values.

Parabola: The shape of the graph of f(x) = ax² + bx + c, a ≠ 0. If the function is written as f(x) = a(x−h)²+k, a 0, then the vertex is (h, k).

Parallel Lines: Two lines in a plane that never intersect.

Parent function: The simplest example of a family of functions.

Perfect Cube: An integer n that can be written in the form n = k³ , where k is an integer.

Perfect Square:

1. An integer n that can be written in the form n = k² , where k is an integer.
2. Also a trinomial which can be written in the form (ax ± b)².

Perpendicular: Lines are perpendicular if they intersect to form a right angle. Segments are perpendicular if the lines containing the segments are perpendicular.

Point-slope form: A form of a linear equation written as (y − y1) = m(x−x1) where m is the slope and the line passes through the point (x1, y1).

Positive Integers: See: Counting Numbers

Power: See: Exponent

Polynomial: A polynomial is an algebraic expression obtained by adding, subtracting and /or multiplying real numbers and variables.

Quadrant: See: Coordinate Plane

Quadratic Equation: An equation with a second degree term as its highest degree term.

Quadratic Expression: A polynomial containing a second degree term as its highest degree term.

Radical: An indicated root of a number or polynomial denoted by n√ so that r = n√x implies r^n = x. The index n is generally omitted when n = 2 and we write √x to mean the square root of x.

Radical Equation: An equation in which the variable appears in the radicand.

Radical Function: A function which is the square root of a variable expression. More generally, a function of the nth root of a variable expression.

Radicand: The number or expression that appears in the radical sign; the number or expression whose root is to be found.

Range: See: Function

Rate:

1. A rate is a division comparison between two quantities with different units of measure. Also see Unit Rate.
2. The amount of interest charged on an annual basis.

Rational Equation: An equation involving one or more rational expressions.

Rational Expression: An expression in the form a/b with a and b being polynomial expressions, b of at least degree one and b 0.

Rational Number: A number that can be written as a/b where a is an integer and b is a natural number.

Reciprocal: See: Multiplicative Inverse

Right Angle: An angle formed by the intersection perpendicular lines; an angle with a measure of 90 deg.

Right Triangle: A triangle that has a right angle.

Roots of a Quadratic: The solutions of ax²+bx+c = 0. The same values are zeros of the quadratic expression or the function f(x) = ax² + bx + c. They are also the x-intercepts of the intersection of the graph of f(x) with the x-axis.

Scale Factor: For the parabola f(x) = a(x−h)² + k, a is the scale factor.

Scientific Notation: Base ten numbers written in the form a × 10^n where 1 ≤ a ≤ 10 and n is an integer.

Sequence: A list of terms ordered by the natural numbers. The outputs of a function whose domain is the natural numbers.

Set: A collection of objects or elements.

Set Notation: A symbolic description of the elements of a set. ”A is the set of all x’s such that x is an element of the natural numbers with x greater than 2 and less than 11” would be written A = {x|x is a natural number , 2 < x < 11}.

Simplifying: Combining like terms of a polynomial by carrying out the indicated additions or subtractions.

Simple Interest: Interest paid a single time on a principal invested or borrowed. Computed using I = Prt.

Simultaneously: See: System of Equations in two Variables

Slope of a Line: If (x1, y1) and (x2, y2) are two points on a line, then the slope of the line is the ratio m =  rise/run = y/x = (y2−y1)/(x2−x1) provided x2  x1

Slope-intercept form: The equation y = mx + b is the slope-intercept form of a line, where m is the slope and b is the y-intercept of the line.

Solution of an Equation: A solution to an equation with variable x is a number that, when substituted for x, makes the two sides of the equation equal. If the equation has more than one solution, then the collection of solutions is called the solution set.

Solution of an Inequality: The values that may be substituted for the variable in an inequality to form a true statement.

Solution of a System of Linear Equations: See System of Linear Equations.

Square Root: For non-negative x and y, y is the square root of x if y² = x. For x a real number, √x² = |x| because the square root symbol denotes the non-negative root.

Square Root Function: See Radical Function.

Standard Form: A form of a linear equation written as Ax +By = C.

Subset: Set B is a subset of set A if every element of set B is also an element of set A.

System of Linear Equations: Two equations that both impose conditions on the variables. An ordered pair is a solution of the system if and only if it is a solution of each of the given equations.

Systems of equations may be classified as follows:

1. A system with one or more solutions is called Consistent.
2. A system with no solution is called Inconsistent.
3. A Consistent system with exactly one solution is called Independent.
4. A Consistent system with more than one solution is called Dependent.

System of inequalities in two variables: Two inequalities that both impose conditions on the variables. If the inequalities form an ”and” statement the solution is all ordered pairs that satisfy both inequalities. If the inequalities form an ”or” statement the solution is any ordered pair that satisfies either inequality.

Term: 1. Each member of a sequence. 2. Each expression in a polynomial separated by addition or subtraction signs.

Translation: A transformation that moves a figure along a line in a plane but does not alter its size or shape. For a parabola, a horizontal or vertical shift in the position of the parent function.

Unit Rate: A ratio of two unlike quantities that has a denominator of 1 unit.

Variable: A letter or symbol that represents an unknown quantity.

Vertex:

1. The common endpoint of two rays forming an angle.
2. The highest or lowest point of the graph of a parabola.

Vertex form of a Parabola: A quadratic function written as f(x) = a(x − h)² + k is in vertex form. The vertex is (h, k) and the coefficient a is the scale factor.

Vertical Axis: See: Coordinate Plane

Whole Numbers: The whole numbers are the numbers in the following never-ending sequence: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, . . .

x-axis: The horizontal axis of a coordinate plane.

x-intercept: The point of intersection of a graph with the x-axis.

y-axis: The vertical axis of a coordinate plane.

y-intercept: The point of intersection of a graph with the y-axis.

Zero power: For any number x, x  0, x^0 = 1.

Zeros of a Quadratic: See Roots of a Quadratic.