# Union and Intersection of sets

1. Feb 3, 2008

### Goldenwind

1. The problem statement, all variables and given/known data
a) Find: $$\bigcup_{i=1}^{\infty}} A_i$$

b) Find: $$\bigcap_{i=1}^{\infty}} A_i$$

Where $A_i$ = (0,i), that is, the set of real numbers x with 0 < x < i

I was doing okay when they gave me $A_i$ = {i, i+1, i+2, ...}, but now that they're giving me (0,i), and introducing x, I'm getting confused.

2. Feb 3, 2008

### Goldenwind

Just noticed that I placed this in the wrong forum. I usually come to the Physics forum, however this time I meant for Calculus.
Tried to find a way to delete or move it, but not finding a way.

If an admin finds this, just delete it. I'll post it in the proper forum.

Apologies.

3. Feb 3, 2008

### CompuChip

Try making a picture. Draw a long line, this is the set of all real numbers. We indicate an open interval (a, b) by putting a bracket ( at the point a, and a bracket ) at the point b. Also see this webpage.
Now draw some intervals (0, 1), (0, 2), (0, 4) and look at their intersection and their union. Post a conjecture about the answer, we'll help you prove it.