Results 1 to 3 of 3

Math Help - relational algebra

  1. #1
    Newbie
    Joined
    Mar 2009
    Posts
    8

    relational algebra

    for the question: Assume that R and S are relations on a set A. Prove
    (using relation-algebraic calculations) or disprove (by providing
    counterexamples) each of the following statements.
    a) If R and S are both reflexive, then R ∪ S is reflexive, too.

    how would i start to answer this question its the syntax of the answer iam having trouble with

    This is what i have R U S = R Subset of S = A<=>A subset of S = Id A subset of S therefore reflexive
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,661
    Thanks
    1616
    Awards
    1
    That same question is answered here.
    http://www.mathhelpforum.com/math-he...l-algebra.html
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2009
    Posts
    8
    hi thanks for the answer that the answer i got but you can't just give the answer with out some explanation.
    A<=>A is =: P(AXA)
    Subset of =: C
    Identity A =: Ia
    And =: ^
    composed of =: o
    This is what i did
    R: A<=>A its definition of reflexive for this is Ia C R
    S: A<=>A its definition of reflexive for this is Ia C S
    (Ia C R) ^ (Ia C S)
    (Ia ^ Ia) C (R ^ S)
    (Ia) C (R ^ S )

    So therefore (Ia) C (R intersect S)

    The question is would i change the or into an intersection or a unison because i remember that unison has the same shape as or and Intersect has the same shape as Or so why in this case does this work or why doesn't it work
    again are there any references anywhere for this material
    Question number 2
    R and S are both reflexive then R o S is reflexive
    So i start the same way.
    R: A<=>A its definition of reflexive for this is Ia C R
    S: A<=>A its definition of reflexive for this is Ia C S

    (Ia C R) ^ (Ia C S)

    Than what? i dunno what to do from this point if you guys can't help that's fine this is really difficult stuff and the resources don't really explain the material well i am hoping to write a book for this and for calculus level 1 and 2 in a way that is understandable with common misconceptions.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: October 26th 2010, 02:22 PM
  2. Relational proof
    Posted in the Discrete Math Forum
    Replies: 7
    Last Post: March 16th 2009, 12:38 PM
  3. Prove with relational algebra
    Posted in the Discrete Math Forum
    Replies: 4
    Last Post: March 10th 2009, 11:13 AM
  4. (Discrete Mathmatics) Defining a relational set
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: March 8th 2009, 06:36 AM
  5. Relational Composition Problem - Please help!
    Posted in the Discrete Math Forum
    Replies: 13
    Last Post: September 10th 2006, 12:51 PM

Search Tags


/mathhelpforum @mathhelpforum