A closed dot on a number line signifies that a particular value is included in a set or interval. It indicates that the endpoint is part of the solution.
For example, if you see a closed dot at the number 3 on a number line, it means that the number 3 is included in whatever range or inequality you are dealing with. This is commonly used in math to represent inequalities. For instance, the inequality x ≤ 3 would be represented with a closed dot at 3, showing that 3 is part of the solution. In contrast, an open dot would mean that the number is not included. This distinction is essential for understanding how to properly interpret mathematical statements regarding sets and intervals.