Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Discrete math

  1. Nov 11, 2005 #1

    How do I proove :

    (A U B) x (A U B) = (A x A) U (B x B)

    if and only if : (A C B) or (B C A) ?

    Please Advice,
    Dimitry Haritonov
  2. jcsd
  3. Nov 11, 2005 #2

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Please show what you've done so far, as per the Guidelines you agreed to.
  4. Nov 12, 2005 #3
    Dear Tom,

    First of all I need to proove the two sides.

    so I've started with first side when ACB:

    (a,b)E(AUB)x(AUB) => aE(AUB) and bE(AUB) => if ACB so AUB=B => aEB and bEB => (a,b)E(BxB)

    the second side:

    (a,b)E(AxA)U(BxB) => here I have a little problem, I don't sure that I can to state that: if ACB so (AxA)U(BxB) = (BXB).

    If It's right, I can continue:


    and we got the same result by the two sides.

    Please Advice,
    Dimitry Haritonov
  5. Nov 13, 2005 #4
    Dear Tom,

    are there any ideas ?

    Please Advice,
    Dimitry Haritonov
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook