Prove if n is an odd integer, then 3n is odd.If the square of an integer is odd, then the integer is oddIf $n^2+10$ is odd then $n$ is odd.Proof that an odd integer multiplied by $3$ and squared is always oddLet c be an integer which is not divisible by 3. Then the equation $x^3 − x = c$ has no integer solutions.Proving that if $n in mathbbZ$ and $n^2 − 6n + 5$ is even, then $n$ must be odd.Prove: if $x$ is even, then $x + 5$ is odd.Prove that $n^4-n^2$ is divisible by $8$ if $n$ is an odd positive integer.Proof: Given that $x$ is a positive integer, prove…Prove that,if $n$ is an integer, then $n^2 + 15n = 1$ is oddProve that $n! > n^3$ for every integer $n ge 6$ using induction

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Prove if n is an odd integer, then 3n is odd.


If the square of an integer is odd, then the integer is oddIf $n^2+10$ is odd then $n$ is odd.Proof that an odd integer multiplied by $3$ and squared is always oddLet c be an integer which is not divisible by 3. Then the equation $x^3 − x = c$ has no integer solutions.Proving that if $n in mathbbZ$ and $n^2 − 6n + 5$ is even, then $n$ must be odd.Prove: if $x$ is even, then $x + 5$ is odd.Prove that $n^4-n^2$ is divisible by $8$ if $n$ is an odd positive integer.Proof: Given that $x$ is a positive integer, prove…Prove that,if $n$ is an integer, then $n^2 + 15n = 1$ is oddProve that $n! > n^3$ for every integer $n ge 6$ using induction






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;








2












$begingroup$


So far I have:



Assume $n$ is odd, $n = 2k+1$ for some integer $k$.



Thenbeginalign3n&= 3(2k+1)\
&= 6k + 3endalign



I'm unsure where to go from here.










share|cite|improve this question











$endgroup$













  • $begingroup$
    Can you find an integer $z$ such that your $3k$ is $3z+1$?
    $endgroup$
    – Ethan Bolker
    9 hours ago










  • $begingroup$
    $6k$ is even. Add $3$ to it gives....
    $endgroup$
    – David G. Stork
    9 hours ago

















2












$begingroup$


So far I have:



Assume $n$ is odd, $n = 2k+1$ for some integer $k$.



Thenbeginalign3n&= 3(2k+1)\
&= 6k + 3endalign



I'm unsure where to go from here.










share|cite|improve this question











$endgroup$













  • $begingroup$
    Can you find an integer $z$ such that your $3k$ is $3z+1$?
    $endgroup$
    – Ethan Bolker
    9 hours ago










  • $begingroup$
    $6k$ is even. Add $3$ to it gives....
    $endgroup$
    – David G. Stork
    9 hours ago













2












2








2





$begingroup$


So far I have:



Assume $n$ is odd, $n = 2k+1$ for some integer $k$.



Thenbeginalign3n&= 3(2k+1)\
&= 6k + 3endalign



I'm unsure where to go from here.










share|cite|improve this question











$endgroup$




So far I have:



Assume $n$ is odd, $n = 2k+1$ for some integer $k$.



Thenbeginalign3n&= 3(2k+1)\
&= 6k + 3endalign



I'm unsure where to go from here.







elementary-number-theory






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited 9 hours ago









José Carlos Santos

204k25 gold badges159 silver badges280 bronze badges




204k25 gold badges159 silver badges280 bronze badges










asked 9 hours ago









Amanda_CAmanda_C

236 bronze badges




236 bronze badges














  • $begingroup$
    Can you find an integer $z$ such that your $3k$ is $3z+1$?
    $endgroup$
    – Ethan Bolker
    9 hours ago










  • $begingroup$
    $6k$ is even. Add $3$ to it gives....
    $endgroup$
    – David G. Stork
    9 hours ago
















  • $begingroup$
    Can you find an integer $z$ such that your $3k$ is $3z+1$?
    $endgroup$
    – Ethan Bolker
    9 hours ago










  • $begingroup$
    $6k$ is even. Add $3$ to it gives....
    $endgroup$
    – David G. Stork
    9 hours ago















$begingroup$
Can you find an integer $z$ such that your $3k$ is $3z+1$?
$endgroup$
– Ethan Bolker
9 hours ago




$begingroup$
Can you find an integer $z$ such that your $3k$ is $3z+1$?
$endgroup$
– Ethan Bolker
9 hours ago












$begingroup$
$6k$ is even. Add $3$ to it gives....
$endgroup$
– David G. Stork
9 hours ago




$begingroup$
$6k$ is even. Add $3$ to it gives....
$endgroup$
– David G. Stork
9 hours ago










6 Answers
6






active

oldest

votes


















3












$begingroup$

Use the fact that $6k+3=2(3k+1)+1$.






share|cite|improve this answer









$endgroup$














  • $begingroup$
    How does the 2(3𝑘+1)+1 help?
    $endgroup$
    – Amanda_C
    9 hours ago










  • $begingroup$
    Because the odd integers are precisely those that can be written as $2N+1$.
    $endgroup$
    – José Carlos Santos
    9 hours ago










  • $begingroup$
    and so that means I can then write 2N + 1 where the N is actually the 3k + 1 ,,,which means its odd and the proof is true?
    $endgroup$
    – Amanda_C
    9 hours ago










  • $begingroup$
    A proof is neither true nor false. But if you add that $6k+3=2(2k+1)+1$, then it will be a correct proof.
    $endgroup$
    – José Carlos Santos
    9 hours ago


















2












$begingroup$

Since $2n$ is even, we have $3n=2n+n$ as a sum of an odd number and an even number, which is obviously odd.






share|cite|improve this answer









$endgroup$






















    1












    $begingroup$

    Take $$n=2k+1$$ this is an odd number, then $$3(2k+1)=6k+3=(6k+2)+1$$ this is also an odd number.






    share|cite|improve this answer









    $endgroup$






















      1












      $begingroup$

      Let $n$ be an odd integer.
      Then $3n$ is the product of two odd integers, and thus odd.






      share|cite|improve this answer











      $endgroup$






















        0












        $begingroup$

        Let $n in mathbbZ$ be odd, so $n = 2m + 1$ for some $m in mathbbZ$. We have:
        beginalign*
        3n = 3(2m+1) = 6m + 3 = 2(3m + 1) + 1,
        endalign*

        where $3m + 1 in mathbbZ$ by closure. Let $z = 3m + 1$, so we have
        beginalign*
        3n = 2z + 1.
        endalign*

        Thus, $3n$ is odd.






        share|cite|improve this answer









        $endgroup$






















          0












          $begingroup$

          $6k + 3$ can be written as $6k + 2 + 1$, now factoring we get $2(3k+1) + 1$, let $(3k+1) = A$, then $2A + 1$ is odd. in general, multiplying an odd integer with an odd integer always yields an odd integer. It is a good idea to prove it, you can also prove it with induction.






          share|cite|improve this answer









          $endgroup$

















            Your Answer








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            6 Answers
            6






            active

            oldest

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            6 Answers
            6






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            3












            $begingroup$

            Use the fact that $6k+3=2(3k+1)+1$.






            share|cite|improve this answer









            $endgroup$














            • $begingroup$
              How does the 2(3𝑘+1)+1 help?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              Because the odd integers are precisely those that can be written as $2N+1$.
              $endgroup$
              – José Carlos Santos
              9 hours ago










            • $begingroup$
              and so that means I can then write 2N + 1 where the N is actually the 3k + 1 ,,,which means its odd and the proof is true?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              A proof is neither true nor false. But if you add that $6k+3=2(2k+1)+1$, then it will be a correct proof.
              $endgroup$
              – José Carlos Santos
              9 hours ago















            3












            $begingroup$

            Use the fact that $6k+3=2(3k+1)+1$.






            share|cite|improve this answer









            $endgroup$














            • $begingroup$
              How does the 2(3𝑘+1)+1 help?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              Because the odd integers are precisely those that can be written as $2N+1$.
              $endgroup$
              – José Carlos Santos
              9 hours ago










            • $begingroup$
              and so that means I can then write 2N + 1 where the N is actually the 3k + 1 ,,,which means its odd and the proof is true?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              A proof is neither true nor false. But if you add that $6k+3=2(2k+1)+1$, then it will be a correct proof.
              $endgroup$
              – José Carlos Santos
              9 hours ago













            3












            3








            3





            $begingroup$

            Use the fact that $6k+3=2(3k+1)+1$.






            share|cite|improve this answer









            $endgroup$



            Use the fact that $6k+3=2(3k+1)+1$.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered 9 hours ago









            José Carlos SantosJosé Carlos Santos

            204k25 gold badges159 silver badges280 bronze badges




            204k25 gold badges159 silver badges280 bronze badges














            • $begingroup$
              How does the 2(3𝑘+1)+1 help?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              Because the odd integers are precisely those that can be written as $2N+1$.
              $endgroup$
              – José Carlos Santos
              9 hours ago










            • $begingroup$
              and so that means I can then write 2N + 1 where the N is actually the 3k + 1 ,,,which means its odd and the proof is true?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              A proof is neither true nor false. But if you add that $6k+3=2(2k+1)+1$, then it will be a correct proof.
              $endgroup$
              – José Carlos Santos
              9 hours ago
















            • $begingroup$
              How does the 2(3𝑘+1)+1 help?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              Because the odd integers are precisely those that can be written as $2N+1$.
              $endgroup$
              – José Carlos Santos
              9 hours ago










            • $begingroup$
              and so that means I can then write 2N + 1 where the N is actually the 3k + 1 ,,,which means its odd and the proof is true?
              $endgroup$
              – Amanda_C
              9 hours ago










            • $begingroup$
              A proof is neither true nor false. But if you add that $6k+3=2(2k+1)+1$, then it will be a correct proof.
              $endgroup$
              – José Carlos Santos
              9 hours ago















            $begingroup$
            How does the 2(3𝑘+1)+1 help?
            $endgroup$
            – Amanda_C
            9 hours ago




            $begingroup$
            How does the 2(3𝑘+1)+1 help?
            $endgroup$
            – Amanda_C
            9 hours ago












            $begingroup$
            Because the odd integers are precisely those that can be written as $2N+1$.
            $endgroup$
            – José Carlos Santos
            9 hours ago




            $begingroup$
            Because the odd integers are precisely those that can be written as $2N+1$.
            $endgroup$
            – José Carlos Santos
            9 hours ago












            $begingroup$
            and so that means I can then write 2N + 1 where the N is actually the 3k + 1 ,,,which means its odd and the proof is true?
            $endgroup$
            – Amanda_C
            9 hours ago




            $begingroup$
            and so that means I can then write 2N + 1 where the N is actually the 3k + 1 ,,,which means its odd and the proof is true?
            $endgroup$
            – Amanda_C
            9 hours ago












            $begingroup$
            A proof is neither true nor false. But if you add that $6k+3=2(2k+1)+1$, then it will be a correct proof.
            $endgroup$
            – José Carlos Santos
            9 hours ago




            $begingroup$
            A proof is neither true nor false. But if you add that $6k+3=2(2k+1)+1$, then it will be a correct proof.
            $endgroup$
            – José Carlos Santos
            9 hours ago













            2












            $begingroup$

            Since $2n$ is even, we have $3n=2n+n$ as a sum of an odd number and an even number, which is obviously odd.






            share|cite|improve this answer









            $endgroup$



















              2












              $begingroup$

              Since $2n$ is even, we have $3n=2n+n$ as a sum of an odd number and an even number, which is obviously odd.






              share|cite|improve this answer









              $endgroup$

















                2












                2








                2





                $begingroup$

                Since $2n$ is even, we have $3n=2n+n$ as a sum of an odd number and an even number, which is obviously odd.






                share|cite|improve this answer









                $endgroup$



                Since $2n$ is even, we have $3n=2n+n$ as a sum of an odd number and an even number, which is obviously odd.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered 9 hours ago









                szw1710szw1710

                6,83712 silver badges23 bronze badges




                6,83712 silver badges23 bronze badges
























                    1












                    $begingroup$

                    Take $$n=2k+1$$ this is an odd number, then $$3(2k+1)=6k+3=(6k+2)+1$$ this is also an odd number.






                    share|cite|improve this answer









                    $endgroup$



















                      1












                      $begingroup$

                      Take $$n=2k+1$$ this is an odd number, then $$3(2k+1)=6k+3=(6k+2)+1$$ this is also an odd number.






                      share|cite|improve this answer









                      $endgroup$

















                        1












                        1








                        1





                        $begingroup$

                        Take $$n=2k+1$$ this is an odd number, then $$3(2k+1)=6k+3=(6k+2)+1$$ this is also an odd number.






                        share|cite|improve this answer









                        $endgroup$



                        Take $$n=2k+1$$ this is an odd number, then $$3(2k+1)=6k+3=(6k+2)+1$$ this is also an odd number.







                        share|cite|improve this answer












                        share|cite|improve this answer



                        share|cite|improve this answer










                        answered 9 hours ago









                        Dr. Sonnhard GraubnerDr. Sonnhard Graubner

                        86k4 gold badges29 silver badges69 bronze badges




                        86k4 gold badges29 silver badges69 bronze badges
























                            1












                            $begingroup$

                            Let $n$ be an odd integer.
                            Then $3n$ is the product of two odd integers, and thus odd.






                            share|cite|improve this answer











                            $endgroup$



















                              1












                              $begingroup$

                              Let $n$ be an odd integer.
                              Then $3n$ is the product of two odd integers, and thus odd.






                              share|cite|improve this answer











                              $endgroup$

















                                1












                                1








                                1





                                $begingroup$

                                Let $n$ be an odd integer.
                                Then $3n$ is the product of two odd integers, and thus odd.






                                share|cite|improve this answer











                                $endgroup$



                                Let $n$ be an odd integer.
                                Then $3n$ is the product of two odd integers, and thus odd.







                                share|cite|improve this answer














                                share|cite|improve this answer



                                share|cite|improve this answer








                                edited 3 hours ago

























                                answered 7 hours ago









                                mlchristiansmlchristians

                                2,0852 silver badges19 bronze badges




                                2,0852 silver badges19 bronze badges
























                                    0












                                    $begingroup$

                                    Let $n in mathbbZ$ be odd, so $n = 2m + 1$ for some $m in mathbbZ$. We have:
                                    beginalign*
                                    3n = 3(2m+1) = 6m + 3 = 2(3m + 1) + 1,
                                    endalign*

                                    where $3m + 1 in mathbbZ$ by closure. Let $z = 3m + 1$, so we have
                                    beginalign*
                                    3n = 2z + 1.
                                    endalign*

                                    Thus, $3n$ is odd.






                                    share|cite|improve this answer









                                    $endgroup$



















                                      0












                                      $begingroup$

                                      Let $n in mathbbZ$ be odd, so $n = 2m + 1$ for some $m in mathbbZ$. We have:
                                      beginalign*
                                      3n = 3(2m+1) = 6m + 3 = 2(3m + 1) + 1,
                                      endalign*

                                      where $3m + 1 in mathbbZ$ by closure. Let $z = 3m + 1$, so we have
                                      beginalign*
                                      3n = 2z + 1.
                                      endalign*

                                      Thus, $3n$ is odd.






                                      share|cite|improve this answer









                                      $endgroup$

















                                        0












                                        0








                                        0





                                        $begingroup$

                                        Let $n in mathbbZ$ be odd, so $n = 2m + 1$ for some $m in mathbbZ$. We have:
                                        beginalign*
                                        3n = 3(2m+1) = 6m + 3 = 2(3m + 1) + 1,
                                        endalign*

                                        where $3m + 1 in mathbbZ$ by closure. Let $z = 3m + 1$, so we have
                                        beginalign*
                                        3n = 2z + 1.
                                        endalign*

                                        Thus, $3n$ is odd.






                                        share|cite|improve this answer









                                        $endgroup$



                                        Let $n in mathbbZ$ be odd, so $n = 2m + 1$ for some $m in mathbbZ$. We have:
                                        beginalign*
                                        3n = 3(2m+1) = 6m + 3 = 2(3m + 1) + 1,
                                        endalign*

                                        where $3m + 1 in mathbbZ$ by closure. Let $z = 3m + 1$, so we have
                                        beginalign*
                                        3n = 2z + 1.
                                        endalign*

                                        Thus, $3n$ is odd.







                                        share|cite|improve this answer












                                        share|cite|improve this answer



                                        share|cite|improve this answer










                                        answered 8 hours ago









                                        Matt.PMatt.P

                                        1,2015 silver badges19 bronze badges




                                        1,2015 silver badges19 bronze badges
























                                            0












                                            $begingroup$

                                            $6k + 3$ can be written as $6k + 2 + 1$, now factoring we get $2(3k+1) + 1$, let $(3k+1) = A$, then $2A + 1$ is odd. in general, multiplying an odd integer with an odd integer always yields an odd integer. It is a good idea to prove it, you can also prove it with induction.






                                            share|cite|improve this answer









                                            $endgroup$



















                                              0












                                              $begingroup$

                                              $6k + 3$ can be written as $6k + 2 + 1$, now factoring we get $2(3k+1) + 1$, let $(3k+1) = A$, then $2A + 1$ is odd. in general, multiplying an odd integer with an odd integer always yields an odd integer. It is a good idea to prove it, you can also prove it with induction.






                                              share|cite|improve this answer









                                              $endgroup$

















                                                0












                                                0








                                                0





                                                $begingroup$

                                                $6k + 3$ can be written as $6k + 2 + 1$, now factoring we get $2(3k+1) + 1$, let $(3k+1) = A$, then $2A + 1$ is odd. in general, multiplying an odd integer with an odd integer always yields an odd integer. It is a good idea to prove it, you can also prove it with induction.






                                                share|cite|improve this answer









                                                $endgroup$



                                                $6k + 3$ can be written as $6k + 2 + 1$, now factoring we get $2(3k+1) + 1$, let $(3k+1) = A$, then $2A + 1$ is odd. in general, multiplying an odd integer with an odd integer always yields an odd integer. It is a good idea to prove it, you can also prove it with induction.







                                                share|cite|improve this answer












                                                share|cite|improve this answer



                                                share|cite|improve this answer










                                                answered 8 hours ago









                                                Donlans DonlansDonlans Donlans

                                                275 bronze badges




                                                275 bronze badges






























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