Questions About Intervals in Calculus for 14 Year Olds

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Discussion Overview

The discussion revolves around understanding intervals in calculus, specifically focusing on the concepts of union and intersection of sets. Participants are exploring the definitions and applications of these concepts as they relate to a specific problem involving the intervals (-3,2] and (1,7].

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant expresses confusion about the notation used in the problem, particularly the meaning of "U" in the context of intervals.
  • Another participant clarifies that "U" represents the union of sets, while questioning if the problem might have intended to ask for the intersection instead.
  • A later reply confirms that the original problem was indeed asking for the intersection, indicating a misunderstanding in the initial interpretation.
  • Participants discuss strategies for remembering the difference between union and intersection, suggesting mnemonic devices.
  • One participant proposes a method of visualizing the problem by drawing a number line to better understand the union and intersection of the intervals.

Areas of Agreement / Disagreement

There is a consensus that the original problem was asking for the intersection of the intervals, although initial confusion existed regarding the notation. However, there is no agreement on the best approach to understand these concepts, as participants offer different methods and explanations.

Contextual Notes

Some participants express uncertainty about the definitions of "open end" and "closed end," as well as the symbols for union and intersection, indicating a need for further clarification on these foundational concepts.

Who May Find This Useful

Students new to calculus, particularly those struggling with the concepts of intervals, union, and intersection, may find this discussion helpful.

Ygmaince241
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Ok, I'm very new to calculus, and was stuck on the very basics of it. I'm only 14, but am extremely interested in math and science. I was inspired to study calculus when reading a book named, "Five Equations that changed the World", by Michael Guillen. Now I was doing some problems involving intervals. The book tells me to sketch the sets. The one problem is (-3,2] U (1, 7]. What exactly does the U stand for? The answer they gave for the example was, (1,2]. I know "(" stands for an open end, and "[" stands for a closed end. How do these apply to the sets. I couldn't see how they got the answer. Please help.
 
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[tex]\cup[/tex] is union.

But are you sure the problem didn't ask for the intersection, (-3, 2] [tex]\cap[/tex] (1, 7], of the intervals...?
 
Last edited:
Ygmaince241 said:
Ok, I'm very new to calculus, and was stuck on the very basics of it. I'm only 14, but am extremely interested in math and science. I was inspired to study calculus when reading a book named, "Five Equations that changed the World", by Michael Guillen. Now I was doing some problems involving intervals. The book tells me to sketch the sets. The one problem is (-3,2] U (1, 7]. What exactly does the U stand for? The answer they gave for the example was, (1,2]. I know "(" stands for an open end, and "[" stands for a closed end. How do these apply to the sets. I couldn't see how they got the answer. Please help.
Like Muzza said, that answer only makes sense if they were asking for the intersection of the two intervals, not the union. I don't exactly understand your problem. Do you understand what "open end", "closed end", "intersection", and "union" mean?
 
Omg, yes. The problem was asking for an intersection. Sorry for not being specific enough.
 
Hey there Ygmaince241.

With the union and intersection symbols it's sometimes a bit hard to remember which is which. I always think of it this way: [tex]\cup[/tex]nion and i[tex]\cap[/tex]tersection.
 
A good way to solve for unions and intersections (if you're really stuck) is to draw a number line with both sets on it. Union is all the numbers in both sets while intersection is the common numbers.
ex.
_____-1_____0_____1___
<~~~~~~~o (-infinity, 0) 0=open, •=closed
•~~~~~~~~~~> [-1, infinity)
Looking at this, you can clearly see that the intersection is [-1, 0) and the union is
(-infinity, infinity)
 

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