Proposition: For all $m, n, p, q$ contained in Natural Numbers, $(m-n)p = mp - np$












0












$begingroup$


I have to prove the following proposition using the axioms for integers, and the definition of subtraction to be $m - n = m + (-n).$



Proof:



$(m-n)p = (m+(-n))p$ by definition of subtraction



$(m+(-n))p = mp + (-n)p$ by Distributivity



$mp + (-n)p = mp - np$ by definition of subtraction



My last line was marked wrong; is this not a valid step to finish the proof?










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$endgroup$












  • $begingroup$
    You need to prove that $(-n)p=-(np)$. You can do that by adding $np $ to each side to get $(-n)p+np=-(np)+np $ so $(-n+n)p=0$ and then you have to prove $0p=0$.
    $endgroup$
    – fleablood
    Feb 3 at 1:34
















0












$begingroup$


I have to prove the following proposition using the axioms for integers, and the definition of subtraction to be $m - n = m + (-n).$



Proof:



$(m-n)p = (m+(-n))p$ by definition of subtraction



$(m+(-n))p = mp + (-n)p$ by Distributivity



$mp + (-n)p = mp - np$ by definition of subtraction



My last line was marked wrong; is this not a valid step to finish the proof?










share|cite|improve this question











$endgroup$












  • $begingroup$
    You need to prove that $(-n)p=-(np)$. You can do that by adding $np $ to each side to get $(-n)p+np=-(np)+np $ so $(-n+n)p=0$ and then you have to prove $0p=0$.
    $endgroup$
    – fleablood
    Feb 3 at 1:34














0












0








0





$begingroup$


I have to prove the following proposition using the axioms for integers, and the definition of subtraction to be $m - n = m + (-n).$



Proof:



$(m-n)p = (m+(-n))p$ by definition of subtraction



$(m+(-n))p = mp + (-n)p$ by Distributivity



$mp + (-n)p = mp - np$ by definition of subtraction



My last line was marked wrong; is this not a valid step to finish the proof?










share|cite|improve this question











$endgroup$




I have to prove the following proposition using the axioms for integers, and the definition of subtraction to be $m - n = m + (-n).$



Proof:



$(m-n)p = (m+(-n))p$ by definition of subtraction



$(m+(-n))p = mp + (-n)p$ by Distributivity



$mp + (-n)p = mp - np$ by definition of subtraction



My last line was marked wrong; is this not a valid step to finish the proof?







elementary-number-theory






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edited Feb 3 at 3:15









J. W. Tanner

4,7871420




4,7871420










asked Feb 3 at 1:23









beepbeepboop123123beepbeepboop123123

606




606












  • $begingroup$
    You need to prove that $(-n)p=-(np)$. You can do that by adding $np $ to each side to get $(-n)p+np=-(np)+np $ so $(-n+n)p=0$ and then you have to prove $0p=0$.
    $endgroup$
    – fleablood
    Feb 3 at 1:34


















  • $begingroup$
    You need to prove that $(-n)p=-(np)$. You can do that by adding $np $ to each side to get $(-n)p+np=-(np)+np $ so $(-n+n)p=0$ and then you have to prove $0p=0$.
    $endgroup$
    – fleablood
    Feb 3 at 1:34
















$begingroup$
You need to prove that $(-n)p=-(np)$. You can do that by adding $np $ to each side to get $(-n)p+np=-(np)+np $ so $(-n+n)p=0$ and then you have to prove $0p=0$.
$endgroup$
– fleablood
Feb 3 at 1:34




$begingroup$
You need to prove that $(-n)p=-(np)$. You can do that by adding $np $ to each side to get $(-n)p+np=-(np)+np $ so $(-n+n)p=0$ and then you have to prove $0p=0$.
$endgroup$
– fleablood
Feb 3 at 1:34










1 Answer
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What you did on the last line was to multiply $(-n)$ with $m$, which is not using the definition of subtraction



I am guessing you have some other principle that states that $(-x)y=(-xy)$, which you can use to justify that:



$mp+(-n)p=mp+(-np)$



And then you use the definition of subtraction to say that:



$mp+(-np)=mp-np$



so that you end up with:



$mp+(-n)p=mp-np$






share|cite|improve this answer









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    1 Answer
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    active

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    1 Answer
    1






    active

    oldest

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    active

    oldest

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    active

    oldest

    votes









    0












    $begingroup$

    What you did on the last line was to multiply $(-n)$ with $m$, which is not using the definition of subtraction



    I am guessing you have some other principle that states that $(-x)y=(-xy)$, which you can use to justify that:



    $mp+(-n)p=mp+(-np)$



    And then you use the definition of subtraction to say that:



    $mp+(-np)=mp-np$



    so that you end up with:



    $mp+(-n)p=mp-np$






    share|cite|improve this answer









    $endgroup$


















      0












      $begingroup$

      What you did on the last line was to multiply $(-n)$ with $m$, which is not using the definition of subtraction



      I am guessing you have some other principle that states that $(-x)y=(-xy)$, which you can use to justify that:



      $mp+(-n)p=mp+(-np)$



      And then you use the definition of subtraction to say that:



      $mp+(-np)=mp-np$



      so that you end up with:



      $mp+(-n)p=mp-np$






      share|cite|improve this answer









      $endgroup$
















        0












        0








        0





        $begingroup$

        What you did on the last line was to multiply $(-n)$ with $m$, which is not using the definition of subtraction



        I am guessing you have some other principle that states that $(-x)y=(-xy)$, which you can use to justify that:



        $mp+(-n)p=mp+(-np)$



        And then you use the definition of subtraction to say that:



        $mp+(-np)=mp-np$



        so that you end up with:



        $mp+(-n)p=mp-np$






        share|cite|improve this answer









        $endgroup$



        What you did on the last line was to multiply $(-n)$ with $m$, which is not using the definition of subtraction



        I am guessing you have some other principle that states that $(-x)y=(-xy)$, which you can use to justify that:



        $mp+(-n)p=mp+(-np)$



        And then you use the definition of subtraction to say that:



        $mp+(-np)=mp-np$



        so that you end up with:



        $mp+(-n)p=mp-np$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Feb 3 at 1:26









        Bram28Bram28

        64.5k44793




        64.5k44793






























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