20050821, 19:43  #1 
"Jason Goatcher"
Mar 2005
3·7·167 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
281_{16} 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
110110110011_{2} 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
2^{2}·3·641 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
1110100100100_{2} 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^{2}×691 Posts 
++ to what Bob said.

20050822, 17:39  #10 
"Richard B. Woods"
Aug 2002
Wisconsin USA
1111000001100_{2} 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. 

Thread Tools  
Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Weird things people search for  Xyzzy  Forum Feedback  9  20160128 03:01 
Some things  Une Personne  Information & Answers  8  20120612 18:10 
question on a few things  science_man_88  Miscellaneous Math  12  20110619 19:50 
Why is the PS3 shaped like a rudder?  E_tron  Hobbies  1  20060519 05:37 
How things are set up...  Xyzzy  Lounge  22  20030810 14:36 