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If A has coordinates (a,b) do you say
My textbook always seems to say 'A is at (a,b)' thanks
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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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...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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I think D is okay, too.
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I in this post= George,Y
I in this post(George,Y)
X'(y-Xβ)=0
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The notation (a,b) can mean a co-ordinate point an open interval. If its a co-ordinate point, you can only say A = (a,b); A ∈ (a,b) and A ⊂ (a,b) wont 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). Its 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 its 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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Thanks it makes sense now
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