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Is this a typo in Section 1.8.1 Mathematics for Computer Science?


How can I learn about proofs for computer science?How can I start to learn proof theory?Proving the existence of a proof without actually giving a proofProof by well ordering: Every positive integer greater than one can be factored as a product of primes.Gentzen and computer scienceElegant demonstration with minimum category theory knowledgeDifferent definitions of Natural Numbers and Proof by ContradictionProve $3^2n-5$ is a multiple of $4$Defining new symbols in a proof, when is this justified?Prove convergence rate to zero increases as n increases













2












$begingroup$


enter image description here



Am I completely mistake or is it suppose to say $n^2$ is a multiple of 2 and therefore $n$ must be a multiple of 4?



This is from MIT's Mathematics for Computer Science










share|cite|improve this question









$endgroup$











  • $begingroup$
    Generally: If $m,n$ are positive integers and $m^1/n$ is not an integer then $m^1/n$ is irrational. Proved by a similar method.
    $endgroup$
    – DanielWainfleet
    Apr 26 at 1:48






  • 1




    $begingroup$
    What makes you think this is a mistake?
    $endgroup$
    – Servaes
    Apr 26 at 7:31















2












$begingroup$


enter image description here



Am I completely mistake or is it suppose to say $n^2$ is a multiple of 2 and therefore $n$ must be a multiple of 4?



This is from MIT's Mathematics for Computer Science










share|cite|improve this question









$endgroup$











  • $begingroup$
    Generally: If $m,n$ are positive integers and $m^1/n$ is not an integer then $m^1/n$ is irrational. Proved by a similar method.
    $endgroup$
    – DanielWainfleet
    Apr 26 at 1:48






  • 1




    $begingroup$
    What makes you think this is a mistake?
    $endgroup$
    – Servaes
    Apr 26 at 7:31













2












2








2


1



$begingroup$


enter image description here



Am I completely mistake or is it suppose to say $n^2$ is a multiple of 2 and therefore $n$ must be a multiple of 4?



This is from MIT's Mathematics for Computer Science










share|cite|improve this question









$endgroup$




enter image description here



Am I completely mistake or is it suppose to say $n^2$ is a multiple of 2 and therefore $n$ must be a multiple of 4?



This is from MIT's Mathematics for Computer Science







proof-explanation proof-theory






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Apr 26 at 1:14









doctopusdoctopus

1414




1414











  • $begingroup$
    Generally: If $m,n$ are positive integers and $m^1/n$ is not an integer then $m^1/n$ is irrational. Proved by a similar method.
    $endgroup$
    – DanielWainfleet
    Apr 26 at 1:48






  • 1




    $begingroup$
    What makes you think this is a mistake?
    $endgroup$
    – Servaes
    Apr 26 at 7:31
















  • $begingroup$
    Generally: If $m,n$ are positive integers and $m^1/n$ is not an integer then $m^1/n$ is irrational. Proved by a similar method.
    $endgroup$
    – DanielWainfleet
    Apr 26 at 1:48






  • 1




    $begingroup$
    What makes you think this is a mistake?
    $endgroup$
    – Servaes
    Apr 26 at 7:31















$begingroup$
Generally: If $m,n$ are positive integers and $m^1/n$ is not an integer then $m^1/n$ is irrational. Proved by a similar method.
$endgroup$
– DanielWainfleet
Apr 26 at 1:48




$begingroup$
Generally: If $m,n$ are positive integers and $m^1/n$ is not an integer then $m^1/n$ is irrational. Proved by a similar method.
$endgroup$
– DanielWainfleet
Apr 26 at 1:48




1




1




$begingroup$
What makes you think this is a mistake?
$endgroup$
– Servaes
Apr 26 at 7:31




$begingroup$
What makes you think this is a mistake?
$endgroup$
– Servaes
Apr 26 at 7:31










2 Answers
2






active

oldest

votes


















3












$begingroup$

No, it is correct. The point is that $2d^2=n^2$ implies $n^2$ is even, and only even numbers square to give an even number, so $n$ much be even, so $n^2$ is then actually a multiple of $4$.






share|cite|improve this answer









$endgroup$












  • $begingroup$
    This makes sense thanks
    $endgroup$
    – doctopus
    2 days ago


















3












$begingroup$

No. $6^2$ is a multiple of $2$ but $6$ is not a multiple of $4$. If $n=2k$ then for sure $n^2=4k^2$. So, MIT is right.






share|cite|improve this answer









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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    3












    $begingroup$

    No, it is correct. The point is that $2d^2=n^2$ implies $n^2$ is even, and only even numbers square to give an even number, so $n$ much be even, so $n^2$ is then actually a multiple of $4$.






    share|cite|improve this answer









    $endgroup$












    • $begingroup$
      This makes sense thanks
      $endgroup$
      – doctopus
      2 days ago















    3












    $begingroup$

    No, it is correct. The point is that $2d^2=n^2$ implies $n^2$ is even, and only even numbers square to give an even number, so $n$ much be even, so $n^2$ is then actually a multiple of $4$.






    share|cite|improve this answer









    $endgroup$












    • $begingroup$
      This makes sense thanks
      $endgroup$
      – doctopus
      2 days ago













    3












    3








    3





    $begingroup$

    No, it is correct. The point is that $2d^2=n^2$ implies $n^2$ is even, and only even numbers square to give an even number, so $n$ much be even, so $n^2$ is then actually a multiple of $4$.






    share|cite|improve this answer









    $endgroup$



    No, it is correct. The point is that $2d^2=n^2$ implies $n^2$ is even, and only even numbers square to give an even number, so $n$ much be even, so $n^2$ is then actually a multiple of $4$.







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered Apr 26 at 1:21









    John DoeJohn Doe

    12.6k11441




    12.6k11441











    • $begingroup$
      This makes sense thanks
      $endgroup$
      – doctopus
      2 days ago
















    • $begingroup$
      This makes sense thanks
      $endgroup$
      – doctopus
      2 days ago















    $begingroup$
    This makes sense thanks
    $endgroup$
    – doctopus
    2 days ago




    $begingroup$
    This makes sense thanks
    $endgroup$
    – doctopus
    2 days ago











    3












    $begingroup$

    No. $6^2$ is a multiple of $2$ but $6$ is not a multiple of $4$. If $n=2k$ then for sure $n^2=4k^2$. So, MIT is right.






    share|cite|improve this answer









    $endgroup$

















      3












      $begingroup$

      No. $6^2$ is a multiple of $2$ but $6$ is not a multiple of $4$. If $n=2k$ then for sure $n^2=4k^2$. So, MIT is right.






      share|cite|improve this answer









      $endgroup$















        3












        3








        3





        $begingroup$

        No. $6^2$ is a multiple of $2$ but $6$ is not a multiple of $4$. If $n=2k$ then for sure $n^2=4k^2$. So, MIT is right.






        share|cite|improve this answer









        $endgroup$



        No. $6^2$ is a multiple of $2$ but $6$ is not a multiple of $4$. If $n=2k$ then for sure $n^2=4k^2$. So, MIT is right.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Apr 26 at 1:19









        RandallRandall

        10.9k11431




        10.9k11431



























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