1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help with proof

  1. Jan 29, 2009 #1
    1. The problem statement, all variables and given/known data
    Prove these propositions


    2. Relevant equations
    If x is rational, then x + sqrt(2) is irrational.
    If x + sqrt(2) is irrational, then x is rational.
    If xsqrt(2) is irrational, then x is rational.

    3. The attempt at a solution
    I've tried a couple of ways, but I always end up at a dead end. usually, I end up assuming what I need to prove.
     
  2. jcsd
  3. Jan 29, 2009 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    The first proposition is true. The others aren't. Can you find a counterexample for them? As to proving the first can you show us what you tried?
     
  4. Jan 29, 2009 #3
    After working with it some more, I've gotten all but the last. Is a counter example something like e(sqrt(2))? But I don't know if that is rational or not.
     
  5. Jan 29, 2009 #4

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    That's too hard. In fact, I'm not sure anybody knows the answer to that. How about sqrt(3)*sqrt(2)?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Help with proof
  1. Help with a proof. (Replies: 10)

  2. Proofs help (Replies: 7)

  3. Help with a proof! (Replies: 8)

  4. Help with a Proof (Replies: 1)

  5. Proof help! (Replies: 3)

Loading...