# Does || symbols inverse?

• May 11th 2010, 12:39 AM
Jarod_C
Does || symbols inverse?
Sorry, a really noobie question but I better ask now instead of later.

I know $\left( \right)$ are grouping symbols, but what are $\left| \right|$ symbols.
• May 11th 2010, 12:51 AM
Bacterius
It means absolute value. Basically, if the number is positive or equals zero, then putting it between | and | does not change its value, whereas if the number if negative, the sign is removed :

$|3| = 3$

$|7| = 7$

$|0| = 0$

$|-2| = 2$

$|-271| = 271$

Careful when analyzing functions using these symbols with an $x$ term in it : you need to consider two different functions : when the expression between the symbol is negative or positive.
• May 11th 2010, 12:55 AM
undefined
Quote:

Originally Posted by Jarod_C
Sorry, a really noobie question but I better ask now instead of later.

I know $\left( \right)$ are grouping symbols, but what are $\left| \right|$ symbols.

There are some different meanings for ||

One is cardinality of a set, so if A = {1,2,4,9,11}, then |A| = 5 because there are 5 elements in A.

One is absolute value, which gives the distance from a real number to 0, so |5| = |-5| = 5.

There are some other uses too. See here and search on the page for "absolute" to find the row entry.
• May 11th 2010, 01:07 AM
Jarod_C
Thanks for your help it cleared up everything. It was hard to ask that simple of a question after two terms of algebra two years ago. Found out I forgot all of it lol
• May 11th 2010, 01:09 AM
Bacterius
One likes being thanked after spending minutes looking up how to write the absolute value symbol on the keyboard, drafting the reply, giving examples and some advice, and finally replying. At least say something if the answer doesn't suit you. It really doesn't encourage further help.

Never mind.
• May 11th 2010, 01:34 AM
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Quote:

Originally Posted by Bacterius
One likes being thanked after spending minutes looking up how to write the absolute value symbol on the keyboard, drafting the reply, giving examples and some advice, and finally replying. At least say something if the answer doesn't suit you. It really doesn't encourage further help.

Never mind.

I used to be active on Yahoo! Answers a long time ago, and it always annoyed me when people gave my posts a "thumbs down" even though my post was correct/valuable/some such. At least there's no thumbs down button on this forum...

It somewhat reminds me of a professor I had who used the term "math(s) by democracy" or "proof by democracy" whereby the solution to a certain problem was decided by vote through show of hands. If the majority voted that a statement is true, isn't that proof enough to make it a theorem? :)
• May 11th 2010, 01:49 AM
Bacterius
Actually there is a "thumbs down" button on this forum. Can you see the little "reputation-o-meter" just left to the "signal post to moderators" triangle ? :D (I'll give you a thumbs up)
• May 11th 2010, 02:01 AM
undefined
Quote:

Originally Posted by Bacterius
Actually there is a "thumbs down" button on this forum. Can you see the little "reputation-o-meter" just left to the "signal post to moderators" triangle ? :D (I'll give you a thumbs up)

Haha, thanks! I had noticed there was a reputation (+) button, but through some sort of tunnel vision I failed to appreciate that there was a (-) button right next to it. (Bigsmile)
• May 11th 2010, 09:23 AM
Jarod_C
Quote:

Originally Posted by Bacterius
One likes being thanked after spending minutes looking up how to write the absolute value symbol on the keyboard, drafting the reply, giving examples and some advice, and finally replying. At least say something if the answer doesn't suit you. It really doesn't encourage further help.

Never mind.

I'm sorry I'm missed your post. I don't know why I skipped right over it. Didn't mean to insult you.