Explanation:
typically, we use the curved parentheses the denote an open interval, so we don't include the extreme values.
for example, the interval (1, 2) will not include 1 and 2. think of it as using the < and > symbols.
on the other hand, we have the boxed parentheses which denote a closed interval, which includes the extreme values.
so, for example [1, 2] would include 1 and 2. think of it as using

signs.
in fact, we can use these signs to explain the intervals better:
![(a, b) \implies a < x < b\\ [a, b] \implies a \leq x \leq b](https://img.qammunity.org/2024/formulas/mathematics/college/aflsead5fn1f2bjo0nx4sw6vupjgo9vnxh.png)
personally, I've seen people use black dots to denote closed intervals and white dots to denote open intervals more often, they mean the same.