Results 1 to 4 of 4

Math Help - Can you help me get started on this proof?

  1. #1
    Junior Member
    Joined
    Sep 2010
    Posts
    48

    Can you help me get started on this proof?

    I'm having trouble on where to begin with this proof. I'm pretty sure it is a valid argument, since I tried to come up with a counter-example but couldn't. I will use the symbol ~ to stand for "not", since I don't know how to make the "not" symbol online.

    Directions: Derive ~Z -> ~Y

    (1) ~X -> Y
    (2) ~X -> Z
    -------------------
    (3) ~Z -> ~(~X).......... (1) Contrapositive


    I think I should start with the contrapositive, but I have no clue where to go from here. Any help would be appreciated
    Last edited by Lprdgecko; September 15th 2010 at 10:58 PM. Reason: Spelling mistake
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    Sep 2010
    Posts
    185
    Thanks
    13
    if ~Z->~(~X) and ~X->Y then ~Z->~Y. Errr... right? Guys?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Oct 2006
    Posts
    71
    Quote Originally Posted by Lprdgecko View Post
    I'm having trouble on where to begin with this proof. I'm pretty sure it is a valid argument, since I tried to come up with a counter-example but couldn't. I will use the symbol ~ to stand for "not", since I don't know how to make the "not" symbol online.

    Directions: Derive ~Z -> ~Y

    (1) ~X -> Y
    (2) ~X -> Z
    -------------------
    (3) ~Z -> ~(~X).......... (1) Contrapositive


    I think I should start with the contrapositive, but I have no clue where to go from here. Any help would be appreciated
    It's not a valid argument.

    Consider the valuation v, where v(Z) = false, and v(Y) = v(X) = true.

    Under v, both premisses are true, and the conclusion is false.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Junior Member
    Joined
    Sep 2010
    Posts
    48
    Quote Originally Posted by PiperAlpha167 View Post
    It's not a valid argument.

    Consider the valuation v, where v(Z) = false, and v(Y) = v(X) = true.

    Under v, both premisses are true, and the conclusion is false.
    Thanks! I could've sworn I tried that counter-example, but I guess not.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. I need help getting started
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: December 14th 2010, 12:02 AM
  2. Need help getting started..
    Posted in the Math Topics Forum
    Replies: 4
    Last Post: October 27th 2010, 03:14 PM
  3. Need help getting started...
    Posted in the Differential Equations Forum
    Replies: 4
    Last Post: June 28th 2010, 04:53 PM
  4. please help get me started on this proof
    Posted in the Discrete Math Forum
    Replies: 3
    Last Post: March 2nd 2010, 08:44 PM
  5. Getting started on proof with primes! Need guidance
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: February 14th 2010, 04:03 PM

Search Tags


/mathhelpforum @mathhelpforum