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Property of summation


Summation signs confusionSummation Indices - How to interpret the zero index?Question about index of summationsReversing the Order of Integration and SummationChanging variable in summationSummation that appears to be zeroHow to explain this summation reordering?Why exchange second summation with (n-i)?How to solve summation from k=0 to n-2?Double summation identity













0












$begingroup$


Very short question. Could you please explain me why



$$sum_i=0^n-1 a = na$$
with $a$ a constant?
I know that



$$sum_i=1^n a = na$$



but in my case the sum starts from zero and finishes for $(n-1)$.



Thanks.










share|cite|improve this question











$endgroup$







  • 7




    $begingroup$
    Sorry, I cannot figure out what is difficult to understand here. Can you enlighten me ?
    $endgroup$
    – Yves Daoust
    10 hours ago











  • $begingroup$
    Recognize that $0,1,2,3,4,dots,n-1$ has $n$ elements in it. If this is not immediately obvious why, then recognize that it has the $n-1$ positive elements $1,2,3,dots,n-1$ and also the one additional zero element $0$. It follows that your summation is iterated a total of $n$ times (the one time when the index is zero, and then the following $n-1$ times while the index is positive for a total of $1+(n-1)=n$ times).
    $endgroup$
    – JMoravitz
    10 hours ago










  • $begingroup$
    Thanks JMoravitz, your rationale was what I needed to convince myself.
    $endgroup$
    – Kolmogorovwannabe
    10 hours ago















0












$begingroup$


Very short question. Could you please explain me why



$$sum_i=0^n-1 a = na$$
with $a$ a constant?
I know that



$$sum_i=1^n a = na$$



but in my case the sum starts from zero and finishes for $(n-1)$.



Thanks.










share|cite|improve this question











$endgroup$







  • 7




    $begingroup$
    Sorry, I cannot figure out what is difficult to understand here. Can you enlighten me ?
    $endgroup$
    – Yves Daoust
    10 hours ago











  • $begingroup$
    Recognize that $0,1,2,3,4,dots,n-1$ has $n$ elements in it. If this is not immediately obvious why, then recognize that it has the $n-1$ positive elements $1,2,3,dots,n-1$ and also the one additional zero element $0$. It follows that your summation is iterated a total of $n$ times (the one time when the index is zero, and then the following $n-1$ times while the index is positive for a total of $1+(n-1)=n$ times).
    $endgroup$
    – JMoravitz
    10 hours ago










  • $begingroup$
    Thanks JMoravitz, your rationale was what I needed to convince myself.
    $endgroup$
    – Kolmogorovwannabe
    10 hours ago













0












0








0





$begingroup$


Very short question. Could you please explain me why



$$sum_i=0^n-1 a = na$$
with $a$ a constant?
I know that



$$sum_i=1^n a = na$$



but in my case the sum starts from zero and finishes for $(n-1)$.



Thanks.










share|cite|improve this question











$endgroup$




Very short question. Could you please explain me why



$$sum_i=0^n-1 a = na$$
with $a$ a constant?
I know that



$$sum_i=1^n a = na$$



but in my case the sum starts from zero and finishes for $(n-1)$.



Thanks.







summation






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited 10 hours ago









MarianD

1,2091614




1,2091614










asked 10 hours ago









KolmogorovwannabeKolmogorovwannabe

257




257







  • 7




    $begingroup$
    Sorry, I cannot figure out what is difficult to understand here. Can you enlighten me ?
    $endgroup$
    – Yves Daoust
    10 hours ago











  • $begingroup$
    Recognize that $0,1,2,3,4,dots,n-1$ has $n$ elements in it. If this is not immediately obvious why, then recognize that it has the $n-1$ positive elements $1,2,3,dots,n-1$ and also the one additional zero element $0$. It follows that your summation is iterated a total of $n$ times (the one time when the index is zero, and then the following $n-1$ times while the index is positive for a total of $1+(n-1)=n$ times).
    $endgroup$
    – JMoravitz
    10 hours ago










  • $begingroup$
    Thanks JMoravitz, your rationale was what I needed to convince myself.
    $endgroup$
    – Kolmogorovwannabe
    10 hours ago












  • 7




    $begingroup$
    Sorry, I cannot figure out what is difficult to understand here. Can you enlighten me ?
    $endgroup$
    – Yves Daoust
    10 hours ago











  • $begingroup$
    Recognize that $0,1,2,3,4,dots,n-1$ has $n$ elements in it. If this is not immediately obvious why, then recognize that it has the $n-1$ positive elements $1,2,3,dots,n-1$ and also the one additional zero element $0$. It follows that your summation is iterated a total of $n$ times (the one time when the index is zero, and then the following $n-1$ times while the index is positive for a total of $1+(n-1)=n$ times).
    $endgroup$
    – JMoravitz
    10 hours ago










  • $begingroup$
    Thanks JMoravitz, your rationale was what I needed to convince myself.
    $endgroup$
    – Kolmogorovwannabe
    10 hours ago







7




7




$begingroup$
Sorry, I cannot figure out what is difficult to understand here. Can you enlighten me ?
$endgroup$
– Yves Daoust
10 hours ago





$begingroup$
Sorry, I cannot figure out what is difficult to understand here. Can you enlighten me ?
$endgroup$
– Yves Daoust
10 hours ago













$begingroup$
Recognize that $0,1,2,3,4,dots,n-1$ has $n$ elements in it. If this is not immediately obvious why, then recognize that it has the $n-1$ positive elements $1,2,3,dots,n-1$ and also the one additional zero element $0$. It follows that your summation is iterated a total of $n$ times (the one time when the index is zero, and then the following $n-1$ times while the index is positive for a total of $1+(n-1)=n$ times).
$endgroup$
– JMoravitz
10 hours ago




$begingroup$
Recognize that $0,1,2,3,4,dots,n-1$ has $n$ elements in it. If this is not immediately obvious why, then recognize that it has the $n-1$ positive elements $1,2,3,dots,n-1$ and also the one additional zero element $0$. It follows that your summation is iterated a total of $n$ times (the one time when the index is zero, and then the following $n-1$ times while the index is positive for a total of $1+(n-1)=n$ times).
$endgroup$
– JMoravitz
10 hours ago












$begingroup$
Thanks JMoravitz, your rationale was what I needed to convince myself.
$endgroup$
– Kolmogorovwannabe
10 hours ago




$begingroup$
Thanks JMoravitz, your rationale was what I needed to convince myself.
$endgroup$
– Kolmogorovwannabe
10 hours ago










6 Answers
6






active

oldest

votes


















8












$begingroup$

Since you are allready convinced that $sum_i=1^na=na$ this might help:



$sum_i=0^n-1a=a+sum_i=1^n-1a=a+sum_i=1^na-a=sum_i=1^na$






share|cite|improve this answer









$endgroup$




















    22












    $begingroup$

    In both cases - $$sum_i=0^n-1aquad text and quadsum_i=1^na$$



    - there are exactly $n$ summands.



    enter image description here






    share|cite|improve this answer









    $endgroup$




















      3












      $begingroup$

      Since $a$ is not $i$-depending one can write: $$sum_i=0^n-1a=asum_i=0^n-11$$
      And $sum_i=0^n-11=1+1+cdots+1$ $n$ times which obviously is $n$.






      share|cite|improve this answer











      $endgroup$




















        2












        $begingroup$

        What is the definition of $sum_i=0^n-1 x_i$? It is exactly $x_0+x_1+...x_n-1$. If $x_0=x_1=...x_n-1=a$ then it means you just sum $a$ $n$ times. And that gives $na$.






        share|cite|improve this answer











        $endgroup$




















          1












          $begingroup$

          You are summing $n$ terms, all equal to $a$. So
          $$sum_i=0^n-1 a = a+ a+dotsb + a = na.$$






          share|cite|improve this answer









          $endgroup$




















            0












            $begingroup$

            Hint:



            $a$ times the number of terms.






            share|cite|improve this answer









            $endgroup$












              Your Answer





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              6 Answers
              6






              active

              oldest

              votes








              6 Answers
              6






              active

              oldest

              votes









              active

              oldest

              votes






              active

              oldest

              votes









              8












              $begingroup$

              Since you are allready convinced that $sum_i=1^na=na$ this might help:



              $sum_i=0^n-1a=a+sum_i=1^n-1a=a+sum_i=1^na-a=sum_i=1^na$






              share|cite|improve this answer









              $endgroup$

















                8












                $begingroup$

                Since you are allready convinced that $sum_i=1^na=na$ this might help:



                $sum_i=0^n-1a=a+sum_i=1^n-1a=a+sum_i=1^na-a=sum_i=1^na$






                share|cite|improve this answer









                $endgroup$















                  8












                  8








                  8





                  $begingroup$

                  Since you are allready convinced that $sum_i=1^na=na$ this might help:



                  $sum_i=0^n-1a=a+sum_i=1^n-1a=a+sum_i=1^na-a=sum_i=1^na$






                  share|cite|improve this answer









                  $endgroup$



                  Since you are allready convinced that $sum_i=1^na=na$ this might help:



                  $sum_i=0^n-1a=a+sum_i=1^n-1a=a+sum_i=1^na-a=sum_i=1^na$







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered 10 hours ago









                  drhabdrhab

                  103k545136




                  103k545136





















                      22












                      $begingroup$

                      In both cases - $$sum_i=0^n-1aquad text and quadsum_i=1^na$$



                      - there are exactly $n$ summands.



                      enter image description here






                      share|cite|improve this answer









                      $endgroup$

















                        22












                        $begingroup$

                        In both cases - $$sum_i=0^n-1aquad text and quadsum_i=1^na$$



                        - there are exactly $n$ summands.



                        enter image description here






                        share|cite|improve this answer









                        $endgroup$















                          22












                          22








                          22





                          $begingroup$

                          In both cases - $$sum_i=0^n-1aquad text and quadsum_i=1^na$$



                          - there are exactly $n$ summands.



                          enter image description here






                          share|cite|improve this answer









                          $endgroup$



                          In both cases - $$sum_i=0^n-1aquad text and quadsum_i=1^na$$



                          - there are exactly $n$ summands.



                          enter image description here







                          share|cite|improve this answer












                          share|cite|improve this answer



                          share|cite|improve this answer










                          answered 10 hours ago









                          MarianDMarianD

                          1,2091614




                          1,2091614





















                              3












                              $begingroup$

                              Since $a$ is not $i$-depending one can write: $$sum_i=0^n-1a=asum_i=0^n-11$$
                              And $sum_i=0^n-11=1+1+cdots+1$ $n$ times which obviously is $n$.






                              share|cite|improve this answer











                              $endgroup$

















                                3












                                $begingroup$

                                Since $a$ is not $i$-depending one can write: $$sum_i=0^n-1a=asum_i=0^n-11$$
                                And $sum_i=0^n-11=1+1+cdots+1$ $n$ times which obviously is $n$.






                                share|cite|improve this answer











                                $endgroup$















                                  3












                                  3








                                  3





                                  $begingroup$

                                  Since $a$ is not $i$-depending one can write: $$sum_i=0^n-1a=asum_i=0^n-11$$
                                  And $sum_i=0^n-11=1+1+cdots+1$ $n$ times which obviously is $n$.






                                  share|cite|improve this answer











                                  $endgroup$



                                  Since $a$ is not $i$-depending one can write: $$sum_i=0^n-1a=asum_i=0^n-11$$
                                  And $sum_i=0^n-11=1+1+cdots+1$ $n$ times which obviously is $n$.







                                  share|cite|improve this answer














                                  share|cite|improve this answer



                                  share|cite|improve this answer








                                  edited 10 hours ago









                                  MarianD

                                  1,2091614




                                  1,2091614










                                  answered 10 hours ago









                                  HAMIDINE SOUMAREHAMIDINE SOUMARE

                                  98929




                                  98929





















                                      2












                                      $begingroup$

                                      What is the definition of $sum_i=0^n-1 x_i$? It is exactly $x_0+x_1+...x_n-1$. If $x_0=x_1=...x_n-1=a$ then it means you just sum $a$ $n$ times. And that gives $na$.






                                      share|cite|improve this answer











                                      $endgroup$

















                                        2












                                        $begingroup$

                                        What is the definition of $sum_i=0^n-1 x_i$? It is exactly $x_0+x_1+...x_n-1$. If $x_0=x_1=...x_n-1=a$ then it means you just sum $a$ $n$ times. And that gives $na$.






                                        share|cite|improve this answer











                                        $endgroup$















                                          2












                                          2








                                          2





                                          $begingroup$

                                          What is the definition of $sum_i=0^n-1 x_i$? It is exactly $x_0+x_1+...x_n-1$. If $x_0=x_1=...x_n-1=a$ then it means you just sum $a$ $n$ times. And that gives $na$.






                                          share|cite|improve this answer











                                          $endgroup$



                                          What is the definition of $sum_i=0^n-1 x_i$? It is exactly $x_0+x_1+...x_n-1$. If $x_0=x_1=...x_n-1=a$ then it means you just sum $a$ $n$ times. And that gives $na$.







                                          share|cite|improve this answer














                                          share|cite|improve this answer



                                          share|cite|improve this answer








                                          edited 9 hours ago

























                                          answered 10 hours ago









                                          MarkMark

                                          10.1k622




                                          10.1k622





















                                              1












                                              $begingroup$

                                              You are summing $n$ terms, all equal to $a$. So
                                              $$sum_i=0^n-1 a = a+ a+dotsb + a = na.$$






                                              share|cite|improve this answer









                                              $endgroup$

















                                                1












                                                $begingroup$

                                                You are summing $n$ terms, all equal to $a$. So
                                                $$sum_i=0^n-1 a = a+ a+dotsb + a = na.$$






                                                share|cite|improve this answer









                                                $endgroup$















                                                  1












                                                  1








                                                  1





                                                  $begingroup$

                                                  You are summing $n$ terms, all equal to $a$. So
                                                  $$sum_i=0^n-1 a = a+ a+dotsb + a = na.$$






                                                  share|cite|improve this answer









                                                  $endgroup$



                                                  You are summing $n$ terms, all equal to $a$. So
                                                  $$sum_i=0^n-1 a = a+ a+dotsb + a = na.$$







                                                  share|cite|improve this answer












                                                  share|cite|improve this answer



                                                  share|cite|improve this answer










                                                  answered 10 hours ago









                                                  HugoHugo

                                                  8206




                                                  8206





















                                                      0












                                                      $begingroup$

                                                      Hint:



                                                      $a$ times the number of terms.






                                                      share|cite|improve this answer









                                                      $endgroup$

















                                                        0












                                                        $begingroup$

                                                        Hint:



                                                        $a$ times the number of terms.






                                                        share|cite|improve this answer









                                                        $endgroup$















                                                          0












                                                          0








                                                          0





                                                          $begingroup$

                                                          Hint:



                                                          $a$ times the number of terms.






                                                          share|cite|improve this answer









                                                          $endgroup$



                                                          Hint:



                                                          $a$ times the number of terms.







                                                          share|cite|improve this answer












                                                          share|cite|improve this answer



                                                          share|cite|improve this answer










                                                          answered 10 hours ago









                                                          Yves DaoustYves Daoust

                                                          130k676229




                                                          130k676229



























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