Formulas, graphs & relations » Domain and range

General

Symbols

< means smaller than
> means greater than
≤ means smaller than or equal to
≥ means greater than or equal to
∞ means infinite
≠ means not equal to

Interval

An interval relates to a certain part of the number line.

x < 5	means that x can be every number smaller than 5.
x ≥ –7	means that x can be every number greater than or equal to –7.
3 ≤ x ≤ 8	means that x can be every number greater than or equal to 3, but smaller than or equal to 8. (x lies between or is equal to 3 and 8)
–2 ≤ x < 0	means that x can be every number greater than or equal to –2, but smaller than 0. (x lies between –2 and 0 or is equal to –2)
3 < x < 8	means that x lies between 3 and 8.
x < 3 or x ≥ 8	means that x can be every number smaller than 3 or greater than or equal to 8.
x ≠ –7	means that x can be every number, except –7.

Other notations

There is more than one way to note down intervals:

	Interval notation
Inequality	Netherlands	US/UK	Belgium
x < 5	〈←, 5〉	(–∞, 5)	]–∞, 5[
x ≥ –7	[–7, →〉	[–7, ∞)	[–7, ∞[
3 ≤ x ≤ 8	[3, 8]	[3, 8]	[3, 8]
–2 ≤ x < 0	[–2, 0〉	[–2, 0)	[–2, 0[
3 < x < 8	〈3, 8〉	(3, 8)	]3, 8[
x < 3 or x ≥ 8	〈←, 3〉 or [8, →〉	(-∞, 3) or [8, ∞)	]-∞, 3[ or [8, ∞[
x ≠ –7	〈←, -7〉 or 〈-7, →〉	(-∞, -7) or (-7, ∞)	]-∞, -7[ or ]-7, ∞[
every x	〈←, →〉	(–∞,∞)	]–∞, ∞[

Domain

The domain of a formula consists of all possible values of x for which the formula has an outcome for y.

Range

The range of a formula consists of every possible outcome, so every possible value of y.

Examples
You can show the graph for each formula by clicking on 'See graph'. The graph will appear underneath the table.

Formula	Domain	Range
y = 3x + 5	every x	every y	See graph
y = 3x2– 2	every x	y ≥ –2	See graph
y =	x ≥ –2	y ≥ –4	See graph
y =	x ≠ 3	y ≠ 1	See graph
y =	x ≤ –4 of x ≥ 4	y ≥ 3	See graph
y =	–4 ≤ x ≤ 4	3 ≤ y ≤ 7	See graph

At square root relation you can find another three examples.