Some people graph the interval by shading it; some people graph the interval by drawing a thicker line segment.

Some people use dots (solid or open) at the endpoints. Some people use grouping symbols (square brackets or parentheses) at the endpoints.

The square brackets have a different meaning than parentheses.

A square bracket denotes that the endpoint value is included in the interval. You could use a solid dot, instead.

A parenthesis denotes that the endpoint value is not included in the interval. You could also use an open dot.

Here are some example descriptions, using dots and shaded segments:

[4, 10)

This interval is a shaded segment that goes from 4 to 10 on the Real number line. The number 4 is included, so there is a solid dot at the left end; the number 10 is not included, so there is an open dot at the right end.

(-500, 500)

This interval is a shaded segment that goes from -500 to 500 on the Real number line. Neither endpoint is included, so there are open dots at each end.

(4/5, 7/5]

This interval is a shaded segment that goes from 4/5 to 7/5 on the Real number line. The number 4/5 is not included, so there is an open dot at the left end; the number 7/5 is included, so there is a solid dot at the right end.

Are you getting the "picture" ?

Here is roughly what the graph of the open interval (25, 100) looks like.

Code:

R
--------O=================O---------->
25 100
OR
R
--------(=================)---------->
25 100