Need some help

1. Jun 23, 2004

Ygmaince241

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. Jun 23, 2004

Muzza

$$\cup$$ is union.

But are you sure the problem didn't ask for the intersection, (-3, 2] $$\cap$$ (1, 7], of the intervals...?

Last edited: Jun 23, 2004
3. Jun 23, 2004

AKG

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?

4. Jun 23, 2004

Ygmaince241

Omg, yes. The problem was asking for an intersection. Sorry for not being specific enough.

5. Jun 23, 2004

Nexus[Free-DC]

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: $$\cup$$nion and i$$\cap$$tersection.

6. Jun 24, 2004

napoleonmax

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)