# When should I use brackets or parenthesis in finding domain

When should I use brackets or parenthesis in finding domain or range?
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Paineow
You should use a bracket (square bracket) to indicate that the endpoint is included in the interval, and a parenthesis (round bracket) to indicate that it is not.
Brackets are like inequalities that say "or equal" and parentheses are like strict inequalities.
For example, (3,7) includes 3.1 and 3.007 and 3.00000000002, but it does not include 3. It also includes numbers greater than 3 and less than 7, but it does not include 7. We can say say this is 3 to 7 "exclusive" (Excluding the endpoints)
[4,9] includes 4 and every number from 4 up to 9, and it also includes 9. We can say this is 4 to 9 "inclusive" (Including the endpoints)
$\left(a,b\right)=\left\{x:a
$\left[a,b\right]=\left\{x:a\le x\phantom{\rule{1em}{0ex}}\text{and}\phantom{\rule{1em}{0ex}}x\le b\right\}$
Of course, there can be also mixed intervals (a,b] or [a,b).
The symbols are used to indicate that there is no left or right endpoint for the interval. They always take parentheses.
For example:
Domain of , $\sqrt{0}=0$ is a number.
Domain of , $\frac{1}{\sqrt{x}}$ is a not number.

Ana Robertson
I'm really grateful, thanks