# help with writing mathsWatch

#1
I need help with a few questions. I've copied the questions and my attempts at them.

1) Turn words into symbols, using standard or Zermelo definitions (or any other symbolic representation).

• The set of rational points in the open unit cube

I've done this: but it looks wrong to me.

2) For each item, provide
(i) a coarse description, which only identiﬁes the class to which
the item belongs (set, function, polynomial, etc.);
(ii) a ﬁner description, which deﬁnes the object in question, or
characterises its structure

sequence, an infinite sequence with increasing terms (is this the right way of wording this?!)

• 13 = (3 + 2√−1)(3 − 2√−1) Is this just a quadratic expression?

an infinite sum of fractions with increasing degree...?

Sorry for all the questions. A bit of help would be appreciated!
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5 years ago
#2
(Original post by #maths)
• The set of rational points in the open unit cube

I've done this: but it looks wrong to me.
A rational point is a point whose coordinates are rational. The ordered triplet is not a rational number.

Have another go.
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#3
(Original post by ghostwalker)
A rational point is a point whose coordinates are rational. The ordered triplet is not a rational number.

Have another go.
I know a point with rational coordinates would be

and the unit cube is

but I don't know how to put them together,

the set of rational points in the open unit cube is this is obviously wrong
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5 years ago
#4
(Original post by #maths)
I know a point with rational coordinates would be
As you noticed the ordered pair (x,y) is not a rational number, it cannot be an element of Q.

BUT it can be an element fo Q^2 - as you posted.

So, just extend that to three coordinates. You're only missing the exponent in your original post.
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5 years ago
#5
(Original post by #maths)
I know a point with rational coordinates would be

and the unit cube is

but I don't know how to put them together,

the set of rational points in the open unit cube is this is obviously wrong
That's the one dimensional version (the open unit interval ). You have already posted the two dimensional version (the open unit square (0,1) \times (0,1)) You want the three dimensional analogue. You were very close at the start.
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3 years ago
#6
We're struggling with the same questions this year. Can you help us please?
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3 years ago
#7
(Original post by maths2015)
We're struggling with the same questions this year. Can you help us please?
Post details of what you've done/tried and where you're stuck.
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3 years ago
#8

Is this correct?
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3 years ago
#9
(Original post by maths2015)

Is this correct?
Nopes, why would be true? Wrong exponent.
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3 years ago
#10
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3 years ago
#11
(Original post by maths2015)
Yups!
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3 years ago
#12
Thank you so much!
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3 years ago
#13
Another question: {x∈R\Q : x2 ∈N} in words.

* Set x is a set of irrational numbers such that x^2 are natural numbers.
Is this correct?
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3 years ago
#14
(Original post by maths2015)
Another question: {x∈R\Q : x2 ∈N} in words.

* Set x is a set of irrational numbers such that x^2 are natural numbers.
Is this correct?
I don't see anything wrong with it.
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3 years ago
#15
Question:
For each item, provide two levels of description: (i) a coarse de- scription, which only identifies the class to which the item belongs (set, function, polynomial, etc.); (ii) a finer description, which defines the object in question, or characterises its structure

For this question can we write 'infinite sequence with increasing terms,?
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3 years ago
#16
(Original post by maths2015)
Question:
For each item, provide two levels of description: (i) a coarse de- scription, which only identifies the class to which the item belongs (set, function, polynomial, etc.); (ii) a finer description, which defines the object in question, or characterises its structure

For this question can we write 'infinite sequence with increasing terms,?
Not necessarily increasing: What about the case x = -1?
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