Finding sets, listing sets (discrete math)

  • Thread starter Chopkilla
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  • #1
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Homework Statement


2. Let A, B and C be the following sets:

A = (x є N | x< 25) B=(x e N | x = 2m for some positive integer m)
C = (x є N | x = 3m for some positive integer m)

Find each of the following sets. In each case, list all of the elements of the set.

i) A – (B u C) ii)A n C



Homework Equations





The Attempt at a Solution



in my last post i have noticed i can't get the answers all done for me (which i understand) so i am pulling an all nighter.. and doind eatch question step by step.. seeing if maybe you all could help me out on this night

A = 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25...
B = 2,4,6,8,10,12,14,16,18,20,22,24
C= 3,6,9,12,15,18,21,24

there for
A= {1,5,7,11,13,17,19,23}

i donm't know how i would write that out clearly.. or even if that is right.. heh
 

Answers and Replies

  • #2
radou
Homework Helper
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A = (x є N | x< 25)

A = 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25...
First of all, what is the difference between the relations '<' and '[itex]\leq[/itex]'?
 
  • #3
HallsofIvy
Science Advisor
Homework Helper
41,833
961

Homework Statement


2. Let A, B and C be the following sets:

A = (x є N | x< 25) B=(x e N | x = 2m for some positive integer m)
C = (x є N | x = 3m for some positive integer m)

Find each of the following sets. In each case, list all of the elements of the set.

i) A – (B u C) ii)A n C



Homework Equations





The Attempt at a Solution



in my last post i have noticed i can't get the answers all done for me (which i understand) so i am pulling an all nighter.. and doind eatch question step by step.. seeing if maybe you all could help me out on this night

A = 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25...
??? You meant "N" didn't you?

B = 2,4,6,8,10,12,14,16,18,20,22,24
C= 3,6,9,12,15,18,21,24
Why are you stopping at 24? The problem tells you that the points in A are less than 25, but not for B and C. (Since the sets you want are subsets of A, this doesn't really change your answer.)

there for
A= {1,5,7,11,13,17,19,23}
Why "therefore"? Yes, this is correct- it follows directly from the definition f A, not what you just wrote.

i donm't know how i would write that out clearly.. or even if that is right.. heh
Assuming that you really meant N for the first, your set A is correct. For B and C, you are missing the "{ }" symbols and need to continue them:
B= {2, 4, 6, 8, 10, 12, 14, 16, 18, ...}
C= {3, 6, 9, 12, 15, ...}

Now, what is "BnC"? What is BuC?
 

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