# Interval Notation

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#### 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.