####
Using Interval Notation

- If an endpoint is included, then use
`[` or `]`.
If not, then use `(` or `)`. For example, the interval
from -3 to 7 that includes 7 but not -3 is expressed `(-3,7]`.

- For infinite intervals, use
`Inf`
for ∞ (infinity) and/or
`-Inf` for -∞ (-Infinity). For
example, the infinite interval containing all points greater than or
equal to 6 is expressed `[6,Inf)`.

- If the set includes more than one interval, they are joined using the union
symbol U. For example, the set consisting of all points in (-3,7] together with all points in [-8,-5) is expressed
`[-8,-5)U(-3,7]`

.

- If the answer is the empty set, you can specify that by using
braces with nothing inside:
` { } `

- You can use
`R`

as a shorthand for all real numbers.
So, it is equivalent to entering `(-Inf, Inf)`

.

- You can use set difference notation. So, for all real numbers
except 3, you can use
`R-{3}`

or
`(-Inf, 3)U(3,Inf)`

(they are the same). Similarly,
`[1,10)-{3,4}`

is the same as `[1,3)U(3,4)U(4,10)`

.

- WeBWorK will
**not** interpret `[2,4]U[3,5]` as equivalent
to `[2,5]`, unless a problem tells you otherwise.
All sets should be expressed in their simplest interval notation form, with no
overlapping intervals.