20050821, 19:43  #1 
"Jason Goatcher"
Mar 2005
5×701 Posts 
Weird Eshaped things(serious question)
I've been wanting to study number theory on my own, but have hit a similar snag in all the books I bought from Amazon. I have encountered two symbols, both approximately shaped like a capital letter E. I am going to describe them and hope that someone can give me a link that can adequately explain one or both of them.
The first symbol looks like a letter c with a horizontal line in the middle. The second is a more jagged E. It has a horizontal line at the top, a line going from the left of the top line diagonally to the middle of the letter space, a line going from the middle to the leftbottom, and a horizontal line going to the right from that last diagonal line. I would really appreciate any help you could give me. thanks 
20050821, 20:12  #2 
"Nancy"
Aug 2002
Alexandria
2,467 Posts 
The symbol ∈ mean "is element of". It refers to sets. I.e. if you have a set S = {1,5,9,11}, then 1∈S, but 2∉S (is not an element of).
The ∑ is the sum symbol. There's ususally a variable name and assignment underneath it, and a limit above, kind of like ∑_{i=1}^{10}, except they are right below/above the ∑. It means that the term following the ∑ is summed with i going from 1 to 10, i.e. ∑_{i=1}^{10} i^2 = 1^2 + 2^2 + 3^2 + 4^2 + 5^2 + 6^2 + 7^2 + 8^2 + 9^2 + 10^2 There's a lot more such notation in mathematics, far more than can be explained in a forum. I'm not familiar with english language texts on this, can someone recommend a book that explains some elementary notation? Alex 
20050821, 20:14  #3 
Jun 2004
UK
139 Posts 
The c sounds like "member of".
See http://en.wikipedia.org/wiki/Member The second sounds like sigma which would mean "sum of". See http://en.wikipedia.org/wiki/Sigma 
20050821, 22:44  #4 
Cranksta Rap Ayatollah
Jul 2003
641 Posts 
Did you look in the back of the book? Usually there's a page explaining notation. If not, find another book that has one

20050821, 22:47  #5 
Cranksta Rap Ayatollah
Jul 2003
641 Posts 
Hmm. This goes the other way (defintion > symbol, not symbol > definition) but it may be helpful to browse: http://mathworld.wolfram.com/topics/Notation.html
ahh, here we go: http://en.wikipedia.org/wiki/Table_o...atical_symbols 
20050822, 00:29  #6 
"Jason Goatcher"
Mar 2005
5·701 Posts 
Thanks anyway, guys. I guess I now know what to look for in a class to take when I go back to college in January, lol!

20050822, 16:12  #7 
"Richard B. Woods"
Aug 2002
Wisconsin USA
7692_{10} Posts 
ANSI Unicode characters, according to one source I have:
(Greek capital letter sigma) Σ (there exists) ∃ (there does not exist) ∄ (element of) ∈ (not an element of) ∉ Last fiddled with by cheesehead on 20050822 at 16:16 
20050822, 16:58  #8  
Nov 2003
2^{3}·7^{2}·19 Posts 
Quote:
these symbols indicates that your high school teachers were grossly negligent or incompetent. How can they not teach their students the symbol for "element of" or "summation"? 

20050822, 17:01  #9 
Aug 2002
Termonfeckin, IE
2,753 Posts 
++ to what Bob said.

20050822, 17:39  #10 
"Richard B. Woods"
Aug 2002
Wisconsin USA
7692_{10} Posts 

20050822, 17:47  #11  
Jun 2003
The Texas Hill Country
3^{2}×11^{2} Posts 
Quote:
Did yours? I do know that it was not a part of my HS math. (in the late '50s) But times have changed ... By the time that I took Algebra in Grad school, they were introducing Sets to Elementary School students. 

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