mersenneforum.org Weird E-shaped things(serious question)
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 2005-08-21, 19:43 #1 jasong     "Jason Goatcher" Mar 2005 3·7·167 Posts Weird E-shaped 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 left-bottom, and a horizontal line going to the right from that last diagonal line. I would really appreciate any help you could give me. thanks
 2005-08-21, 20:12 #2 akruppa     "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=110, 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=110 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
 2005-08-21, 20:14 #3 marc     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
 2005-08-21, 22:44 #4 Orgasmic Troll 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
 2005-08-21, 22:47 #5 Orgasmic Troll Cranksta Rap Ayatollah     Jul 2003 28116 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
 2005-08-22, 00:29 #6 jasong     "Jason Goatcher" Mar 2005 1101101100112 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!
 2005-08-22, 16:12 #7 cheesehead     "Richard B. Woods" Aug 2002 Wisconsin USA 22·3·641 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 2005-08-22 at 16:16
2005-08-22, 16:58   #8
R.D. Silverman

Nov 2003

11101001001002 Posts

Quote:
 Originally Posted by jasong 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!
May I ask where you attended high school? Your failure to recognize
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"?

 2005-08-22, 17:01 #9 garo     Aug 2002 Termonfeckin, IE 22×691 Posts ++ to what Bob said.
2005-08-22, 17:47   #11
Wacky

Jun 2003
The Texas Hill Country

32×112 Posts

Quote:
 Originally Posted by R.D. Silverman May I ask where you attended high school? Your failure to recognize 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"?
Bob,

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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