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Why is this equality with sums and monomials true?



The Next CEO of Stack OverflowMultinomial theorem: Number of elements where all coefficients have even powers..Artin-Chevalley Theorem.Relation between roots an coefficients in a generic equation: $a_0+a_1cdot x+cdots+a_ncdot x^n$Polynomial function in several variablesWhen is $X_1^a_1 cdots X_n^a_n-1$ irreducible?Why should this ideal be maximal?Solving system of equations with sums of odd powerAlgebraic identity involving partitions of indexesTrouble with understanding the definition of cyclic sums?Definition of a valuation of a rational fraction










0












$begingroup$


Consider $$(x_1 + ... + x_n)^k = sum_alphac_alphax^alpha$$ where $x^alpha = x_1^a_1cdots x_n^a_n$ and $|alpha| = a_1 + ... + a_n$.



Why is this true? Is it something to do with the binomial sum?










share|cite|improve this question









$endgroup$











  • $begingroup$
    Actually, it's multinomial rather than binomial.
    $endgroup$
    – Robert Israel
    Mar 27 at 18:56






  • 1




    $begingroup$
    Don't you want to say what the $c_alpha$ are?
    $endgroup$
    – Lord Shark the Unknown
    Mar 27 at 19:02















0












$begingroup$


Consider $$(x_1 + ... + x_n)^k = sum_alphac_alphax^alpha$$ where $x^alpha = x_1^a_1cdots x_n^a_n$ and $|alpha| = a_1 + ... + a_n$.



Why is this true? Is it something to do with the binomial sum?










share|cite|improve this question









$endgroup$











  • $begingroup$
    Actually, it's multinomial rather than binomial.
    $endgroup$
    – Robert Israel
    Mar 27 at 18:56






  • 1




    $begingroup$
    Don't you want to say what the $c_alpha$ are?
    $endgroup$
    – Lord Shark the Unknown
    Mar 27 at 19:02













0












0








0





$begingroup$


Consider $$(x_1 + ... + x_n)^k = sum_alphac_alphax^alpha$$ where $x^alpha = x_1^a_1cdots x_n^a_n$ and $|alpha| = a_1 + ... + a_n$.



Why is this true? Is it something to do with the binomial sum?










share|cite|improve this question









$endgroup$




Consider $$(x_1 + ... + x_n)^k = sum_alphac_alphax^alpha$$ where $x^alpha = x_1^a_1cdots x_n^a_n$ and $|alpha| = a_1 + ... + a_n$.



Why is this true? Is it something to do with the binomial sum?







polynomials summation binomial-theorem






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Mar 27 at 18:54









the manthe man

831716




831716











  • $begingroup$
    Actually, it's multinomial rather than binomial.
    $endgroup$
    – Robert Israel
    Mar 27 at 18:56






  • 1




    $begingroup$
    Don't you want to say what the $c_alpha$ are?
    $endgroup$
    – Lord Shark the Unknown
    Mar 27 at 19:02
















  • $begingroup$
    Actually, it's multinomial rather than binomial.
    $endgroup$
    – Robert Israel
    Mar 27 at 18:56






  • 1




    $begingroup$
    Don't you want to say what the $c_alpha$ are?
    $endgroup$
    – Lord Shark the Unknown
    Mar 27 at 19:02















$begingroup$
Actually, it's multinomial rather than binomial.
$endgroup$
– Robert Israel
Mar 27 at 18:56




$begingroup$
Actually, it's multinomial rather than binomial.
$endgroup$
– Robert Israel
Mar 27 at 18:56




1




1




$begingroup$
Don't you want to say what the $c_alpha$ are?
$endgroup$
– Lord Shark the Unknown
Mar 27 at 19:02




$begingroup$
Don't you want to say what the $c_alpha$ are?
$endgroup$
– Lord Shark the Unknown
Mar 27 at 19:02










1 Answer
1






active

oldest

votes


















0












$begingroup$

You can consider it related to the binomial sum, as any multinomial, can be rewritten as nested binomials. However it's technical name is the multinomial sum. Consider the trinomial power $$(a+b+c)^3$$. It can be rewritten as $$(a+(b+c))^3$$ because of the associative property of addition, which is then a binomial power with $$b+c=d$$ Expanding once, we get:$$a^3+3da^2+3ad^2+d^3$$, which follows the binomial sum of exponents rule. Expanding the powers of d, will also not break the binomial exponent sum rule (d is a binomial after all). Therefore expanding it fully, the whole thing will not break the exponent sum rule. We then get:$$a^3+3ba^2+3ca^2+3ab^2+6abc+3ac^2+b^3+3cb^2+3bc^2+c^3$$






share|cite|improve this answer









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    1 Answer
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    active

    oldest

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    active

    oldest

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    0












    $begingroup$

    You can consider it related to the binomial sum, as any multinomial, can be rewritten as nested binomials. However it's technical name is the multinomial sum. Consider the trinomial power $$(a+b+c)^3$$. It can be rewritten as $$(a+(b+c))^3$$ because of the associative property of addition, which is then a binomial power with $$b+c=d$$ Expanding once, we get:$$a^3+3da^2+3ad^2+d^3$$, which follows the binomial sum of exponents rule. Expanding the powers of d, will also not break the binomial exponent sum rule (d is a binomial after all). Therefore expanding it fully, the whole thing will not break the exponent sum rule. We then get:$$a^3+3ba^2+3ca^2+3ab^2+6abc+3ac^2+b^3+3cb^2+3bc^2+c^3$$






    share|cite|improve this answer









    $endgroup$

















      0












      $begingroup$

      You can consider it related to the binomial sum, as any multinomial, can be rewritten as nested binomials. However it's technical name is the multinomial sum. Consider the trinomial power $$(a+b+c)^3$$. It can be rewritten as $$(a+(b+c))^3$$ because of the associative property of addition, which is then a binomial power with $$b+c=d$$ Expanding once, we get:$$a^3+3da^2+3ad^2+d^3$$, which follows the binomial sum of exponents rule. Expanding the powers of d, will also not break the binomial exponent sum rule (d is a binomial after all). Therefore expanding it fully, the whole thing will not break the exponent sum rule. We then get:$$a^3+3ba^2+3ca^2+3ab^2+6abc+3ac^2+b^3+3cb^2+3bc^2+c^3$$






      share|cite|improve this answer









      $endgroup$















        0












        0








        0





        $begingroup$

        You can consider it related to the binomial sum, as any multinomial, can be rewritten as nested binomials. However it's technical name is the multinomial sum. Consider the trinomial power $$(a+b+c)^3$$. It can be rewritten as $$(a+(b+c))^3$$ because of the associative property of addition, which is then a binomial power with $$b+c=d$$ Expanding once, we get:$$a^3+3da^2+3ad^2+d^3$$, which follows the binomial sum of exponents rule. Expanding the powers of d, will also not break the binomial exponent sum rule (d is a binomial after all). Therefore expanding it fully, the whole thing will not break the exponent sum rule. We then get:$$a^3+3ba^2+3ca^2+3ab^2+6abc+3ac^2+b^3+3cb^2+3bc^2+c^3$$






        share|cite|improve this answer









        $endgroup$



        You can consider it related to the binomial sum, as any multinomial, can be rewritten as nested binomials. However it's technical name is the multinomial sum. Consider the trinomial power $$(a+b+c)^3$$. It can be rewritten as $$(a+(b+c))^3$$ because of the associative property of addition, which is then a binomial power with $$b+c=d$$ Expanding once, we get:$$a^3+3da^2+3ad^2+d^3$$, which follows the binomial sum of exponents rule. Expanding the powers of d, will also not break the binomial exponent sum rule (d is a binomial after all). Therefore expanding it fully, the whole thing will not break the exponent sum rule. We then get:$$a^3+3ba^2+3ca^2+3ab^2+6abc+3ac^2+b^3+3cb^2+3bc^2+c^3$$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered yesterday









        Roddy MacPheeRoddy MacPhee

        573118




        573118



























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