When should parentheses be used and when should brackets be used?

Question

Solving Linear Inequalities- what do parentheses indicate and what do brackets indicate? For example the interval notations (a,b], or [a,5], or (a,b). I don't understand how to determine which symbol of inclusion to use and when.

Answer 1

In interval notation round brackets (parentheses) are used for strictly less or greater than (that is, < or >). Square brackets are used for ≤ or ≥. The former is an exclusive interval while the latter is an inclusive interval. Infinity or negative infinity is always exclusive (parenthesis) when part of an interval.

Example: 1<x<3 is represented by the interval (1,3) while 1<x≤3 is represented by (1,3].

-∞<x<∞ is a boundless interval represented by (-∞,∞).