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
-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.