去心邻域 | 玄数

2012-01-28

1.   区间(Interval)

 区间是数的集合。设 a、b 都是实数,且 a < b

(1)闭区间(Closed Interval): [a,b] = {x | a ≤ x ≤ b},a∈[a,b], b∈[a,b]

(2)开区间(Open Interval): (a,b) = {x | a < x < b},a ∉ (a,b), b ∉ (a,b)

(3)半开区间(Half-closed Interval):[a,b) = {x | a ≤ x < b},a∈[a,b), b ∉ [a,b)

(4)半开区间(Half-closed Interval):(a,b] = {x | a < x ≤b},a ∉ (a,b],b∈(a,b]

Interval

a、b叫做区间的端点,在数轴上表示时:包含为实心,不包含则为空心。b – a 是区间的长度。
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