Interval Notation for Set Intersection and Union

In summary, when finding the intersection of two intervals, A and B, the resulting interval will only contain the numbers that are common between A and B. In the example given, the intersection of A and B is (3,5). Similarly, the intersection of A and C is [-3,5), as C is a subset of A. The book's answers for A\cap B and A\cap C are likely referring to the union instead of the intersection.
  • #1
rudders93
46
0

Homework Statement


Consider the following intervals:

A = [-3,5), B = (3,8), C = (0,4]

Find: A[itex]\cap[/itex]B and A[itex]\cap[/itex]C

The Attempt at a Solution



I thought that: A[itex]\cap[/itex]B=(3,5) and that A[itex]\cap[/itex]C=[0,4] as that is the intersection point, but this book (Schaum's Probability Outlines) says that A[itex]\cap[/itex]B=[-3,8) and A[itex]\cap[/itex]C=[-3,5)

I'm looking to confirm that the book might be wrong (Amazon reviews indicate a lot of typographical errors) and instead maybe their answer refers to [itex]A\cup B[/itex] and [itex]A\cup C[/itex] perhaps? Or am I getting confused?

Thanks!
 
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  • #2
The book answers are for union [itex]\cup[/itex], and you are really close to correct with your answers for intersection [itex]\cap[/itex]. It could be a typo in either question or answer.
 
  • #3
Yes, [itex]A\cap B= (3, 5)[/itex] while [itex]A\cup B= [-3, 8)[/itex] as Joffan says. [itex]A\cup C= [-3, 5)[/itex]. But [itex]A\cap C[/itex] is NOT [0, 4] because 0 is not in C.
In fact, C is a subset of A so [itex]A\cap C= C[/itex] and [itex]A\cup C= A[/itex].
 

1. What is short hand interval notation?

Short hand interval notation is a method of representing intervals on a number line using two numbers separated by a comma. The first number represents the lower bound of the interval, and the second number represents the upper bound. The notation is typically written as [a, b] or (a, b) depending on whether the endpoints are included or excluded.

2. How is short hand interval notation different from set notation?

Short hand interval notation is a more compact and simplified way of representing intervals compared to set notation. Set notation uses a combination of inequalities and union/intersection symbols to represent intervals, whereas short hand interval notation uses only two numbers to represent the bounds of the interval.

3. Can short hand interval notation be used for both open and closed intervals?

Yes, short hand interval notation can be used for both open and closed intervals. An open interval is represented as (a, b), where the endpoints are excluded, while a closed interval is represented as [a, b], where the endpoints are included.

4. How do you represent infinity in short hand interval notation?

In short hand interval notation, infinity can be represented using the symbol or -∞ depending on whether the interval is unbounded from above or below. For example, an interval from 5 to positive infinity would be written as [5, ∞).

5. Can short hand interval notation be used for non-numerical values?

No, short hand interval notation is specifically used for representing numerical intervals on a number line. It cannot be used for non-numerical values such as words or symbols.

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