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Acute Angle

An angle that measures less than 90 degrees

Adjacent Angles

Angles in the same plane that have a common vertex and a common side


A figure formed by two rays with a common endpoint called the vertex


The number of square units needed to cover a given surface


The sum of the items in a set of data divided by the number of items in the set; also called mean


The set of all points in a plane that are the same distance from a given point called the center


The distance around a circle


A method used to estimate a sum when all addends are close to the same value

Complementary Angles

Two angles whose measures add to 90 degrees

Composite Number

A number greater than 1 that has more than two whole-number factors


Having the same size and shape

Cross Product

The product of numbers on the diagonal when comparing two ratios

Customary System

The measurement system often used in the United States


The bottom number of a fraction that tells how many equal parts are in the whole


A line segment that passes through the center of a circle and has endpoints on the circle, or the length of that segment


The result when one number is subtracted from another


The number to be divided in a division problem


Can be divided by a number without leaving a remainder


The number you are dividing by in a division problem


A point at the end of a line segment or ray

Expanded Form

A number written as the sum of the values of its digits


The number that indicates how many times the base is used as a factor


A number that is multiplied by another number to get a product

GCF (Greatest Common Factor)

The largest common factor of two or more given numbers

Improper Fraction

A fraction in which the numerator is greater than or equal to the denominator

Indirect Measurement

The technique of using similar figures and proportions to find a measure


A member of the set of whole numbers and their opposites

Intersecting Lines

Lines that cross at exactly one point


The space between marked values on a number line or the scale of a graph

Inverse Operations

Operations that undo each other: addition and subtraction, or multiplication or division

LCD (Least common denominator)

The least common multiple of two or more denominators

LCM (Least common multiple)

The smallest number, other than zero, that is a multiple of two or more given numbers

Like Fractions

Fractions that have the same denominator


A straight path that extends without end in opposite directions

Line of Reflection

A line that a figure is figure is flipped across to create a mirror image of the original figure

Line of Symmetry

The imaginary "mirror" in line symmetry


The sum of the items in a set of data divided by the number of items in the set; also called average


The middle number or the mean (average) of the two middle numbers in an ordered set of data

Metric System

A decimal system of weights and measures that is used universally in science and commonly throughout the world

Mixed Number

A number made up of a whole number that is not zero and a fraction


The number or numbers that occur most frequently in a set of data; when all numbers occur with the same frequency, we say there is no mode


A multiple of a number is the product of the number and any nonzero whole number

Negative Number

A number less than zero


An arrangement of two-dimensional figures that can be folded to form a polyhedron


The top number of a fraction that tells how many parts of a whole are being considered

Obtuse Angle

An angle whose measure is greater than 90 degrees but less than 180 degrees

Odd Number

A whole number that is not divisible by two


Two numbers that are an equal distance from zero on a number line

Order of Operations

A rule for evaluating expressions: first perform the operations in parentheses, then compute powers and roots, then perform all multiplication and division from left to right, and then perform all addition and subtraction from left to right

Parallel Lines

Lines in a place that do not intersect


A ratio comparing a number to 100


The distance around a polygon

Perpendicular Lines

Lines that intersect to form right angles


The ratio of the circumference of a circle to the length of its diameter; 3.14 or 22/7


A flat surface that extends forever


An exact location in space


A closed plane figure formed by three or more line segments that intersect only at their endpoints


A three-dimensional figure in which all the surfaces or faces are polygons

Positive Number

A number greater than zero

Prime Factorization

A number written as the product of its prime factors

Prime Number

A whole number greater than 1 that has exactly two factors, itself and 1


A polyhedron that has two congruent, polygon-shaped bases and other faces that are all rectangles


The result when two or more numbers are multiplied


An equation that states that two ratios are equivalent


A tool for measuring angles


A polyhedron with a polygon base and triangular sides that all meet at a common vertex


The x- and y-axes divide the coordinate plane into four regions. Each region is called a quadrant.


The result when one number is divided by another


A line segment with one endpoint at the center of a circle and the other endpoint on the circle, or the length of that segment


The difference between the greatest and least values in a data set


A ratio that compares two quantities measured in different units


A comparison of two quantities by division


One of two numbers whose product is 1


A transformation of a figure that flips the figure across a line

Regular Polygon

A polygon with congruent sides and angles


A transformation in which a figure is turned around a point

Scientific Notation

A method of writing very large or very small numbers by using powers of 10


Figures with the same shape but not necessarily the same size are similar

Skew Lines

Lines that lie in different planes that are neither parallel nor intersecting

Straight Angle

An angle that measures 180 degrees


The result when two or more numbers are added

Supplementary Angles

Two angles whose measures have a sum of 180 degrees

Surface Area

The sum of the areas of the faces, or surfaces, of a three-dimensional figure


A change in the size or position of a figure


A movement (slide) of a figure along a straight line


A symbol used to represent a quantity that can change


On an angle or polygon, the point where two sides intersect

Vertical Angles

A pair of opposite congruent angles formed by intersecting lines


The number of cubic units needed to fill a given space

Zero Pair

A number and its opposite, which add to 0

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