Answer:
When we have an empty circle in a point, this means that the value of the point is not included.
This would be used for something like:
x > a
The value a is not a solution, because x needs to be larger than a, then we should use the empty circle.
A filled circle is used when the value is included in the solutions.
This is used for inequalities like:
x ≥ a
Where x = a is a possible solution.
Then if we have te set:
Z ≥ 3
We should have a filled circle at the value 3.
