Homework Help: Set theory help !

1. Oct 16, 2012

Andrax

we have E=(a+b)/ab (a,b)EN*
1/ prove that E C ]0,2] (i already duid that )
2/ is ]0,2] E E? shelp me in this one!

2. Relevant equations

3. The attempt at a solution
x $\in$ ]0,2] $\Rightarrow$ x $\in$ E

2. Oct 16, 2012

LCKurtz

If E=(a+b)/ab what does EN* mean? What does ]0,2]E E mean? Please state your problem with proper notation.

3. Oct 16, 2012

Staff: Mentor

E means $\in$ and N* means the positive integers, I believe.
I second that.

4. Oct 17, 2012

Andrax

well sorry didn't find the proper notations in the advanced mode umm any solution?

5. Oct 17, 2012

Staff: Mentor

You can use ε in the top row of Quick Symbols (on the right after you click Go Advanced). Or you can use LaTeX: [ itex ] \in [ /itex ] (without the spaces).

Also, tell us what you meant by N*.

6. Oct 17, 2012

Ray Vickson

You could try using words:
E = {(a+b)/(ab): a,b positive integers}. And "is ]0,2] a subset of E?"
or
E = {(a+b)/(ab): a,b,in N*}, and "is ]0,2] subset E?"

RGV

7. Oct 18, 2012

Andrax

I want to prove that ]0,2 is a subset of E E = {(a+b)/(ab): a,b,in N*}, and "is ]0,2] subset E?"

8. Oct 18, 2012

LCKurtz

Aren't all the numbers in E rational?

9. Oct 18, 2012

HallsofIvy

In other words, you want to show that if $0< x\le 2$, the x= (a+ b)/(ab) for some positive integers a and b. $\sqrt{2}$ lies between 0 and 2 doesn't it?

10. Oct 19, 2012

Andrax

yes it does what's your point?

11. Oct 19, 2012

Andrax

ohh i get your point wow that's really easy dunno how i missed it