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# interval notation help?

i have to find the interval notation which represents the set of all numbers from 2 through 7, inclusive. I do not know what

(

and

[

mean. Can someone explain it to me? And what do they mean inclusive? Thanks a ton! =]

### 2 Answers

- 1 decade agoFavorite Answer
Yay! Something I can answer with 100% confidence.

[ ] mean they include the numbers inside the brackets. For example, [1,10] means: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

( ) means not including the numbers within the brackets. For example: (1, 10) means: 2, 3, 4, 5, 6, 7, 8, 9

So for your questions:

2 through 7 inclusive means: [2,7] the numbers 2 and 7 are part of the set

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- 1 decade ago
[2,7]

inclusive means that it includes the numbers at the end of the range also. when you use the brackets [ ], that means those numbers are included.

when you use the parenthesis ( ), the numbers are not.

So: [2,7] includes the #s: 2, 3, 4, 5, 6, 7

(2,7) includes the #s: 3, 4, 5, 6

(2,7] would include the #s: 3, 4, 5, 6, 7

MORE:

you can use a U to signify gaps between the numbers.

Say you want to have include #s from 3-9, inclusive and 13-20, inclusive, you can write that as [3,9] U [13,20].

(on a number line you would use closed and open circles.)

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