A square bracket shows that the endpoint belongs to the set, while a parenthesis shows that it does not. This distinction corresponds to whether an inequality includes equality, such as less than or equal to versus strictly less than. Reading the endpoint symbols correctly prevents solution sets from including or excluding boundary values incorrectly.
Infinity is written with a parenthesis because it does not represent a finite real endpoint that can belong to a set. Thus, an interval extending toward infinity remains open in that direction, regardless of whether its finite endpoint is included. This convention distinguishes unbounded behavior from an interval that ends at an actual real number.
A union is appropriate when the solution contains two or more separate ranges rather than one continuous interval. Each range is written individually, with its own endpoint conventions, and the union symbol connects them. This format preserves gaps between solution regions and communicates the complete set without implying that missing values are included.
First identify the boundary value or values where the inequality changes condition. Use a bracket when the boundary satisfies the inequality and a parenthesis when it does not. If the solution continues without bound, use infinity with a parenthesis. For separated solution regions, write each interval and connect them with a union.
For a function, interval notation can record the input values allowed in its domain or the output values produced in its range. Endpoint symbols indicate whether boundary values are included, while unions can represent separated portions of either set. This gives a concise way to communicate restrictions and support graph interpretation.
In calculus and analysis, interval notation specifies the real-number regions used when discussing continuity, optimization, or integration. Its endpoint conventions clarify whether a boundary is part of the region under consideration, and unbounded notation describes ranges extending indefinitely. These details help state assumptions and interpret conclusions accurately within a defined interval.