Interval Notation
a way of writing the set of all real numbers between two endpoints. the symbols [ and ] are used to include an endpoint in an interval, and the symbols ( and ) are used to exclude an endpoint from an interval

closed interval
denoted by [a,b] which contains all real numbers and a≤x≤b

open interval
denoted by (a,b) which contains all real numbers x and a<x<b

half open half closed intervals
are (a,b] consists of all real numbers x were a<x≤b, & [a,b) consists of all real numbers x were a≤x<b

left endpoint
denoted by a

right endpoint
denoted by b

∞
infinity not a real number but a symbol that represents unboundedness in a positive direction; not included in endpoints since not a real number

-∞
negative infinity not a real number but a symbol that represents unboundedness in a negative direction; not included in endpoints since not a real number

[a,∞)
consists of all real numbers x for which x≥a

(a,∞)
consists of all real numbers x for which x>a

(-∞,a]
consists of all real numbers x for which x≤a

(-∞,a)
consists of all real numbers x for which x<a

(-∞,∞)
consists of all real numbers x

a^2
any number squared is never a negative integer

relation
correspondence between two sets

x→y
x corresponds to y or y dends on x

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