Results 1 to 3 of 3

Thread: how is this possible without using example....by proving

  1. #1
    rcs
    rcs is offline
    Senior Member rcs's Avatar
    Joined
    Jul 2010
    From
    iligan city. Philippines
    Posts
    484
    Thanks
    2

    how is this possible without using example....by proving

    1.)If a|bc then a|c
    let a = 2 and b = 5 and c = 20

    so (5)(20) / 2 = 50
    then 20/2 = 10


    what if we let a = 3 b= 7 c = 4
    (7)(4)/3 = 28/3 = has a remainder... will this be considered true?



    2.)if a|c and b|c then ab|c

    let a = 2 and b = 5 and c = 20
    so 20/2 = 10 and 20/5 = 4 then 20/(2)(5) = 20/10 = 2

    what if we let a = 3 b= 7 c = 4
    4/3 = 2 and 4/7 = has remainder... will this be considered true?


    How can we prove this ... please help.... thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Nov 2013
    From
    California
    Posts
    5,595
    Thanks
    2359

    Re: how is this possible without using example....by proving

    1) is untrue

    consider $a=3, c=2, b=6$

    $a | 12$ but $a \not | 2$

    2) is untrue

    consider $a=3, b=6, c=12$

    $3 | 12,~6|12,~18 \not | 12$
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    12,811
    Thanks
    1921

    Re: how is this possible without using example....by proving

    It's not true.

    a = 9, b = 3 and c = 6 is a counterexample.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Proving
    Posted in the Calculus Forum
    Replies: 1
    Last Post: Jun 12th 2011, 06:09 AM
  2. Proving gcd(5^98 + 3, 5^99 +1 ) = 14
    Posted in the Algebra Forum
    Replies: 1
    Last Post: Aug 5th 2010, 01:16 PM
  3. Proving an identity that's proving to be complex
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: Jul 21st 2009, 01:30 PM
  4. Proving
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: Mar 27th 2008, 08:27 PM
  5. More Proving
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: Mar 27th 2008, 05:04 PM

/mathhelpforum @mathhelpforum