Inequality symbols and number line
Four symbols, two types of endpoint.
| Symbol | Meaning | Endpoint on number line |
|---|---|---|
| less than | OPEN circle (hollow) | |
| greater than | OPEN circle (hollow) | |
| less than or equal to | CLOSED circle (filled) | |
| greater than or equal to | CLOSED circle (filled) |
Use:
- OPEN when the endpoint is NOT included.
- CLOSED when the endpoint IS included.
Compound inequalities combine two conditions:
- : is strictly greater than AND less than or equal to .
Interval notation is an alternative:
- : open interval, neither endpoint included.
- : closed interval, both endpoints included.
- : closed on left, open on right.
- : all numbers . Infinity is always open (you can't 'reach' it).
- : open circle.
- : closed circle.
- Shaded line shows the solution range.
- Interval notation: closed, open.