Glossary Entries

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Obtuse Angle An angle that has a value greater than 90 degrees and less than 180 degrees.
Obtuse Triangle A triangle that contains one obtuse angle.
Octagon A polygon with 8 sides and 8 angles.
Odd Number A number that when divided by two gives a remainder of positive or negative 1. Examples are 1, 3, 5, 7 and 9. It is represented by a number that has 1,3,5,7, or 9 in the ones position.
One-Digit Number A number consisting of just one digit. Examples: 0, 1,2,3,4,5,6,7,8, or 9.
Ones Place The first digit to the left of the decimal point; it shows how many ones are in a number. It is also called the ones position.
One-Step Equation An equation or inequality that can be solved in one step or action.
One-to-One Correspondence The relationship between the spoken word and the written symbol.
Open Figure A figure that is not closed; i.e., it does not start and end at the same point.
Open Sentence A statement that contains at least one unknown. It becomes true or false when a quantity is substituted for the unknown. Example: 4 + n= 5 becomes true when n = 1.
Operation The action in a math problem. An operation can be addition, subtraction, multiplication, or division. Procedures used to combine numbers, expressions, or polynomials into a single result.
Opposite The result of taking a number and changing its sign (e.g., the opposite of 5 is –5, the opposite of –12 is –(–12) or 12; a number and its opposite are equidistant from zero in a number line, but on opposite sides of zero.(See additive inverse)
Order To place numbers or objects in a sequential arrangement (e.g., least to greatest or heaviest to lightest).
Order of Operations A specified sequence in which mathematical operations are expected to be performed. An arithmetic expression is evaluated by following these ordered steps: (1) simplify within grouping symbols such as parentheses or brackets, starting with the innermost; (2) apply exponents - powers and roots; (3) perform all multiplications and divisions in order from left to right; (4) perform all additions and subtractions in order from left to right.
Ordered Pair A set of two numbers named in an order that matters; represented by (x,y) such that the first number, x, represents the x-coordinate and the second number, y, represents the y-coordinate when the ordered pair is graphed on the coordinate plane; each point on the coordinate plane has a unique ordered pair associated with it.
Ordinal Number A whole number that names the position of an object in sequence. First, second, and third are ordinal numbers.
Ordinate The Y coordinate on a Cartesian graph. The Cartesian system is the one that looks like a grid full of squares.
Origin The point on the coordinate plane where the x- and y-axes intersect; has coordinates (0,0).
Ounce A customary unit used to measure mass; 1 ounce = 1/16 pound; 16 ounces = 1 pound. The abbreviation for ounce is "oz."
Outcome One of the possible events in a probability experiment (e.g., when tossing a fair coin there are two possible outcomes, heads or tails).
Outlier A number in a set of data that is much larger or smaller than most of the other numbers in the set. Example: In the data set {3, 5, 4, 4, 6, 2, 25, 5, 6, 2} the value of 25 is an outlier.


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