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#1 2007-07-30 01:18:25

Identity
Member
Registered: 2007-04-18
Posts: 934

Coordinates question

If A has coordinates (a,b) do you say




?

My textbook always seems to say 'A is at (a,b)' rolleyes thanks

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#2 2007-07-30 01:22:46

Ricky
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Registered: 2005-12-04
Posts: 3,791

Re: Coordinates question

A = (a, b) means that A is a point at (a, b).

A ∈ (a, b) means that A is a scalar with a < A < b.

A being a subset of (a, b) means that A is a set containing only members that satisfy a < x < b.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#3 2007-07-30 12:02:57

krassi_holmz
Real Member
Registered: 2005-12-02
Posts: 1,905

Re: Coordinates question

...and A(a,b) means that the coordinates of A are a and B, as you may have seen r(O,R) - a circle with radius R and origin O.


IPBLE:  Increasing Performance By Lowering Expectations.

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#4 2007-08-01 15:58:46

George,Y
Member
Registered: 2006-03-12
Posts: 1,379

Re: Coordinates question

I think D is okay, too.

Like
I in this post= George,Y
I in this post(George,Y)


X'(y-Xβ)=0

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#5 2007-08-01 21:25:26

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

Re: Coordinates question

The notation (a,b) can mean a co-ordinate point an open interval. If it’s a co-ordinate point, you can only say A = (a,b); A ∈ (a,b) and A ⊂ (a,b) won’t make any sense at all.

On the other hand, if (a,b) refers to an interval, then A = (a,b), A ∈ (a,b) and A ⊂ (a,b) all make sense, depending on what exactly A is. However, intervals have nothing to do with co-ordinate points – so this is probably not what you want.

Your textbook is not wrong. You can say “A is at (a,b)”, even if it sounds just a little more awkward than “A = (a,b)”. It’s like saying “my address is at number 18 <insert road name here>” rather than “my address is number 18 <road name>”; neither, strictly speaking, is wrong.

A(a,b) is usable, but unlike the other three it’s not a statement on its own. It may be used as part of a statement, e.g.: “A(a,b) is a fixed point.”

Last edited by JaneFairfax (2007-08-01 21:25:46)

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#6 2007-08-01 22:44:39

Identity
Member
Registered: 2007-04-18
Posts: 934

Re: Coordinates question

Thanks it makes sense now

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