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# How do you know when to use brackets or parentheses in finding domain or range?

Last updated date: 02nd Aug 2024
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We can write the domain and range in interval notation, which uses values within brackets to describe a set of numbers. In interval notation, we use a square bracket $\left[ {} \right]$ when the set includes the endpoint and a parenthesis $\left( {} \right)$ to indicate that the endpoint is either not included or the interval is unbounded.
We take an arbitrary value a. if $a\in \left( x,y \right)$ then it means $x < a < y$ and if $a\in \left[ x,y \right]$ then it means $x\le a\le y$.
In real number cases we can say that $4\notin \left( 4,5 \right)$ but $4\in \left[ 4,5 \right]$. Same thing can be said about the number 5.
The use of the brackets and parentheses also describes the inclusiveness and exclusiveness. There are two more combined ways to express the inclusion and exclusion of endpoints. These are $\left[ {} \right),\left( {} \right]$. These are mixed forms.