O

octagon

A polygon with eight sides.

page 99

one-dimensional object

An object made up of pieces of lines and curves.

ones

Our number system is based on ten digits (numbers). Using the ten digits, a number can be written. The place where each number is written tells its value. The first place or column from the right is called the ones place. For example, in the number 762, the 2 represents a quantity of two.

pages 70, 71–77, 78–83, 126–127, 130–132, 142, 161, 171–183, 367–369

open number sentence

A number sentence with a value missing. That value needs to be found to make the number sentence true.
5 + 6 = _____ + 3
5 + 5 + _____ = 5 + 7

operation

A process that takes two numbers and results in a third. For example, addition, subtraction, multiplication, and division are operations.

pages 243, 284–286

ordered pair

A pair of numbers that gives the coordinates of a point on a grid in relation to the origin. The horizontal coordinate is given first; the vertical coordinate is given second. For example, the ordered pair (5, 2) tells us to move five units to the right of the origin and 2 units up.

page 326

origin

The point at which the x-axis (horizontal) and y-axis (vertical) intersect on a coordinate plane. The origin is described by the ordered pair (0, 0) and serves as a reference point.

pages 324–326, 327–329, 341, 347