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!

Direct proofs help

  1. Jun 12, 2012 #1
    1. The problem statement, all variables and given/known data

    Let nεZ,Prove that 1-n^2>0, then 3n-2 is an even integer.

    2. Relevant equations



    3. The attempt at a solution

    I proved it like this. I think its right but im not able to word it correctly.

    Since 1-n^2>0 therefore n=0. Then 3n-6=3(0)-6=-6. Since 0 is an integer, 3n-6 is even.

    How can I learn to word this correctly because im having some trouble with it?
     
  2. jcsd
  3. Jun 12, 2012 #2
    Try posting in the number theory forum, this isn't really calculus.
     
  4. Jun 12, 2012 #3
    this is intro to proofs actually. Im trying to self study.
     
  5. Jun 12, 2012 #4
  6. Jun 12, 2012 #5
    I wouldn't worry too much about proper wording as long as you get the concept. n has to equal zero and -6 is an even integer...sounds proved to me. :)

    Although, you probably shouldn't take my advice. I'm shunned by many in academia due to my deep detestation of pretentiousness. ;)
     
  7. Jun 12, 2012 #6

    Mark44

    Staff: Mentor

    The above is confusing. A better statement would be
    Let n ##\in## Z. If 1 - n2 > 0, then show that 3n - 2 is an even integer.
    Note that you have a typo in your work. You're supposed to prove that 3n - 2 is an even integer.

    I would say it like this:
    Since 1 - n2 > 0 and n ##\in## Z, then n = 0.
    So 3n - 2 = - 2, which is an even integer.

    Therefore, for any integer n, if 1 - n2 > 0, then 3n - 2 is an even integer.

    It should NOT be posted in the number theory section. That section and the other sections under Mathematics are not for homework and homework-type problems

    No, here is probably fine, although the Precalc Mathematics section would also be a good choice.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Direct proofs help
  1. Direct Proof (Replies: 1)

  2. Direct Sum Proof (Replies: 1)

  3. Simple Direct Proof (Replies: 3)

Loading...