Glossary - Oo

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.