<p>In the present paper we give all complete decompositions over <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\mathbb {C}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">C</mi> </math></EquationSource> </InlineEquation> of the polynomial <Equation ID="Equ68"> <EquationSource Format="TEX">\(\begin{aligned} P(x)=(x-a_1)^{k_1}\cdots (x-a_m)^{k_m}, \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <mi>P</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo>-</mo> <msub> <mi>a</mi> <mn>1</mn> </msub> <mo stretchy="false">)</mo> </mrow> <msub> <mi>k</mi> <mn>1</mn> </msub> </msup> <mo>⋯</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo>-</mo> <msub> <mi>a</mi> <mi>m</mi> </msub> <mo stretchy="false">)</mo> </mrow> <msub> <mi>k</mi> <mi>m</mi> </msub> </msup> <mo>,</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(2\le m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <mo>≤</mo> <mi>m</mi> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(m\notin \left\{ 4, 6, 7, 10\right\} \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>∉</mo> <mfenced close="}" open="{"> <mn>4</mn> <mo>,</mo> <mn>6</mn> <mo>,</mo> <mn>7</mn> <mo>,</mo> <mn>10</mn> </mfenced> </mrow> </math></EquationSource> </InlineEquation> is a positive integer, <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(a_1, a_2, \ldots , a_m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>a</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>a</mi> <mn>2</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>a</mi> <mi>m</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> are pairwise distinct real numbers, <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(k_1,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>k</mi> <mn>1</mn> </msub> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(k_2,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>k</mi> <mn>2</mn> </msub> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\ldots ,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>…</mo> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(k_m\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>k</mi> <mi>m</mi> </msub> </math></EquationSource> </InlineEquation> are positive integers and the number of pairwise distinct integers among <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(k_1, k_2,\ldots , k_m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>k</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>k</mi> <mn>2</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>k</mi> <mi>m</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> is greater than <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\((m+1)/2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>m</mi> <mo>+</mo> <mn>1</mn> <mo stretchy="false">)</mo> <mo stretchy="false">/</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>. As a consequence, we prove that if <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(a_1, a_2, \ldots , a_m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>a</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>a</mi> <mn>2</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>a</mi> <mi>m</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> are pairwise distinct rational numbers and <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(f(x)\in \mathbb {Q}[x]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> <mo>∈</mo> <mi mathvariant="double-struck">Q</mi> <mo stretchy="false">[</mo> <mi>x</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> is an irreducible polynomial over <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(\mathbb {Q}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">Q</mi> </math></EquationSource> </InlineEquation>, then under certain conditions related to the exponents <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(k_1, k_2, \ldots , k_m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>k</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>k</mi> <mn>2</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>k</mi> <mi>m</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> and the degree of the polynomial <i>f</i>(<i>x</i>), the polynomial <Equation ID="Equ69"> <EquationSource Format="TEX">\(\begin{aligned} P(x)=f(x)^n(x-a_1)^{k_1}\cdots (x-a_m)^{k_m} \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <mi>P</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>f</mi> <msup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mi>n</mi> </msup> <msup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo>-</mo> <msub> <mi>a</mi> <mn>1</mn> </msub> <mo stretchy="false">)</mo> </mrow> <msub> <mi>k</mi> <mn>1</mn> </msub> </msup> <mo>⋯</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo>-</mo> <msub> <mi>a</mi> <mi>m</mi> </msub> <mo stretchy="false">)</mo> </mrow> <msub> <mi>k</mi> <mi>m</mi> </msub> </msup> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>is always indecomposable over the field of complex numbers.</p>

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Indecomposability of the polynomials \(P(x)=f(x)^n(x-a_1)^{k_1}\cdots (x-a_m)^{k_m}\)

  • Csaba Rakaczki

摘要

In the present paper we give all complete decompositions over \(\mathbb {C}\) C of the polynomial \(\begin{aligned} P(x)=(x-a_1)^{k_1}\cdots (x-a_m)^{k_m}, \end{aligned}\) P ( x ) = ( x - a 1 ) k 1 ( x - a m ) k m , where \(2\le m\) 2 m , \(m\notin \left\{ 4, 6, 7, 10\right\} \) m 4 , 6 , 7 , 10 is a positive integer, \(a_1, a_2, \ldots , a_m\) a 1 , a 2 , , a m are pairwise distinct real numbers, \(k_1,\) k 1 , \(k_2,\) k 2 , \(\ldots ,\) , \(k_m\) k m are positive integers and the number of pairwise distinct integers among \(k_1, k_2,\ldots , k_m\) k 1 , k 2 , , k m is greater than \((m+1)/2\) ( m + 1 ) / 2 . As a consequence, we prove that if \(a_1, a_2, \ldots , a_m\) a 1 , a 2 , , a m are pairwise distinct rational numbers and \(f(x)\in \mathbb {Q}[x]\) f ( x ) Q [ x ] is an irreducible polynomial over \(\mathbb {Q}\) Q , then under certain conditions related to the exponents \(k_1, k_2, \ldots , k_m\) k 1 , k 2 , , k m and the degree of the polynomial f(x), the polynomial \(\begin{aligned} P(x)=f(x)^n(x-a_1)^{k_1}\cdots (x-a_m)^{k_m} \end{aligned}\) P ( x ) = f ( x ) n ( x - a 1 ) k 1 ( x - a m ) k m is always indecomposable over the field of complex numbers.