Results 1 to 2 of 2

Math Help - Prime number proff

  1. #1
    Newbie
    Joined
    Oct 2009
    Posts
    24

    Prime number proff

    If p is an odd prime (doesn't equal 5), prove that (p^2)+1 or (p^2)-1 is divisible by 10.

    I appreciate the help.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Oct 2009
    From
    New York, NY
    Posts
    6

    Sketch of proof

    Here is a sketch of the proof you'll need. I'm assuming it was an odd prime you're looking for, as 2 does not work, thus:

    Let p be an odd prime not equal to 5. Then p is either congruent to 1, 3, 7, or 9 modulo 10. squaring any of these numbers we see that they are congruent to either 1 or 9 modulo 10, so if we add 1 or subtract 1, respectively, they are congruent to 0 modulo 10, thus divisible by 10.

    Hope that helps.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 0
    Last Post: September 24th 2011, 11:23 AM
  2. Replies: 1
    Last Post: September 2nd 2009, 08:31 AM
  3. prime number
    Posted in the Number Theory Forum
    Replies: 1
    Last Post: September 23rd 2008, 05:02 PM
  4. Prime number
    Posted in the Number Theory Forum
    Replies: 6
    Last Post: September 6th 2008, 08:21 AM
  5. Number theory, prime number
    Posted in the Number Theory Forum
    Replies: 1
    Last Post: September 17th 2006, 08:11 PM

Search Tags


/mathhelpforum @mathhelpforum