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#226 Re: Help Me ! » Periodic function » 2007-04-02 03:45:15

The first one  , since


The Period is

#227 Re: Help Me ! » Help » 2007-04-02 02:21:10

OH!!!!!!! You can replace

  NEVER THOUGHT OF THAT!!!!

#229 Re: Help Me ! » Help » 2007-04-01 21:36:26

I checked my book , it said the answer is 


Like this one
, But the answer said it's
,HELPP!!!!PP!!P!

#231 Re: Help Me ! » I need help with Bijections! » 2007-04-01 16:05:35

If A={1,2,3} the bi-function is  2x+1 , then B={3,5,7}

If P(x)=(x-1)(x-2)(x-3)
Then P(A)={0} , P(B)={0,24,120}

I think this statement is a little weird.

#232 Help Me ! » Help » 2007-04-01 14:53:53

Stanley_Marsh
Replies: 5

I have trouble with second derivative , I am not sure if I have skipped some

important rules , please help me step by step or point out my error.

here is what I did with (1)

#233 Re: Help Me ! » Set Theory Again » 2007-04-01 13:21:50

Yah , right , your method shows that whatever S_n be , there is a y to avoid it.

#234 Re: Help Me ! » Set Theory Again » 2007-04-01 09:57:21

What I wanted to do was , to show that there is always one new real number  between two real number  , if the set of real is countable, then between two element , there is always a new element in Real , but not in the set , contradict with the definition of the set which contains all real numbers. thus real number is uncountable.

#235 Re: Help Me ! » Set Theory Again » 2007-03-31 21:15:58

The proof of Rational being countable is given in the book

#236 Re: Help Me ! » Set Theory Again » 2007-03-31 21:14:16

this question is from the Rudin's book , he just simply mention   there is a one-to-one correspondence between S and N if S is countable, and that is .It's more like a handbook than a textbook.
  and I haven't learned about Cantor's diagonal argument  ,About proving the open interval (0, 1) is uncountable , Can I do it this way?
  Assume it's countable then the set


   I am borrowing the Euclid's proving there are infinite primes method.

#237 Help Me ! » Set Theory Again » 2007-03-31 19:40:02

Stanley_Marsh
Replies: 7

Prove whether the set of all  irrational real numbers countable.

I think it's uncountable

Then I think the set of rational number is countable and closed

then its complement the set of irrational is open , thus uncountable.

I don't know If I have misunderstood these math concepts.

Please give a proof

#238 Re: Help Me ! » Question for Set theory fans~:) » 2007-03-31 19:29:37

I am looking for some thing about Differential Geometry now .  I always learn some from here and some from there , never go deep into one.

#239 Re: Help Me ! » Dividing Fractions » 2007-03-31 13:54:48

all you need to do , is to put the divisor up side down and multiply

#240 Re: Help Me ! » Question for Set theory fans~:) » 2007-03-31 13:49:05

I am interested in finding the explanation for space time , black hole sth like that.

#241 Re: Help Me ! » Question for Set theory fans~:) » 2007-03-31 11:40:06

Yah , I am going to try that one , thank you .  and , I always wanted to learn Theoretical Physics someday , do u know what kind of math , I have to be equiped with?

#242 Re: Help Me ! » Question for Set theory fans~:) » 2007-03-31 02:22:06

My book is Principles Of Mathematical Analysis by Walter Rudin , and I find his proofs very confusing .  Thanks again!

#243 Re: Help Me ! » Question for Set theory fans~:) » 2007-03-30 20:41:37

Did you guys feel confused at the first time? the whole thing is so abstract , my textbook doesnt have a graph and  I have to learn it by myself .

#244 Re: Help Me ! » Question for Set theory fans~:) » 2007-03-30 20:32:47

Thanks a lots . But like this kind of expression metric space (M, d), What does it mean , I've never seen it before.

#245 Help Me ! » Question for Set theory fans~:) » 2007-03-30 09:48:57

Stanley_Marsh
Replies: 14

I am really confused about basic topology, What does it mean by E is closed if every limit point of E is a point of E.

and  How to use the notation of neighborhood to prove things .

Suppose

where X is a metric space , how can E be relative to Y and not to X at the same time.

#246 Re: Help Me ! » train me quick!!! » 2007-03-29 12:22:53

you mean which field in math? Geometry? Algebra? or ....?

#247 Re: Help Me ! » weird prove and exercises with 3 unknows » 2007-03-29 02:54:38

Here is what I think about the second
First ,

rearrange it , get

Obviously

Then


And


Then ...Still working on it.

#248 Re: Help Me ! » vector cross product » 2007-03-28 13:29:09

I dont think you did wrong ,  cuz  4(3,0,4)=(12,0,16)

#249 Re: Help Me ! » weird prove and exercises with 3 unknows » 2007-03-28 10:06:58

Too many unknown , I use trick to eliminate them , I dont know if it's correct tho.

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