Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need some help

  1. Jun 23, 2004 #1
    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.
  2. jcsd
  3. Jun 23, 2004 #2
    [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: Jun 23, 2004
  4. Jun 23, 2004 #3


    User Avatar
    Science Advisor
    Homework Helper

    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?
  5. Jun 23, 2004 #4
    Omg, yes. The problem was asking for an intersection. Sorry for not being specific enough.
  6. Jun 23, 2004 #5
    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.
  7. Jun 24, 2004 #6
    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.
    <~~~~~~~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)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook