March 10th, 2011, 02:19 PM  #1 
Member Joined: Nov 2010 Posts: 78 Thanks: 0  Set Statements
I would appreciate help with the following problem: A := {3x : x is an element of the Natural numbers} B := {3x+21 : x is an element of the Natural numbers} C := {x+7 : x is an element of the Natural numbers} E := {x : x is an element of the Natural numbers} F := {3x21 : x is an element of the Natural numbers} Are the following statements true? Need proof or why it is false. A intersect E = B A intersect C = B E intersect F = A Thanks for the help! 
March 10th, 2011, 02:23 PM  #2 
Global Moderator Joined: Nov 2009 From: Northwest Arkansas Posts: 2,766 Thanks: 4  Re: Set Statements
A is a subset of E, so A^E (intersect) is just A. Now the question is reduced to "A = B". They are not equal. Look for the smallest elements of each, and demonstrate that there is an element in (either A or B) that is not in the other. 
March 10th, 2011, 03:00 PM  #3 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms  Re: Set Statements
Moved to Set Theory.


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