How to find multiplicity of eigenvalues?












0












$begingroup$


So i have this matrix:



enter image description here



Sorry for the formatting, I'm new here and any help would be great.



We compute the characteristic polynomial



$p(lambda)= {rm det}(A − lambda I d)= (lambda + 2)^2 (1 − λ)$



So from here I know that one of the root is 1 and the other one is -2. However, it states on the answer sheet that the multiplicity of -2 is 2 ? How come ? I don't see two -2 roots in the equation .



Somebody please help?










share|cite|improve this question











$endgroup$

















    0












    $begingroup$


    So i have this matrix:



    enter image description here



    Sorry for the formatting, I'm new here and any help would be great.



    We compute the characteristic polynomial



    $p(lambda)= {rm det}(A − lambda I d)= (lambda + 2)^2 (1 − λ)$



    So from here I know that one of the root is 1 and the other one is -2. However, it states on the answer sheet that the multiplicity of -2 is 2 ? How come ? I don't see two -2 roots in the equation .



    Somebody please help?










    share|cite|improve this question











    $endgroup$















      0












      0








      0





      $begingroup$


      So i have this matrix:



      enter image description here



      Sorry for the formatting, I'm new here and any help would be great.



      We compute the characteristic polynomial



      $p(lambda)= {rm det}(A − lambda I d)= (lambda + 2)^2 (1 − λ)$



      So from here I know that one of the root is 1 and the other one is -2. However, it states on the answer sheet that the multiplicity of -2 is 2 ? How come ? I don't see two -2 roots in the equation .



      Somebody please help?










      share|cite|improve this question











      $endgroup$




      So i have this matrix:



      enter image description here



      Sorry for the formatting, I'm new here and any help would be great.



      We compute the characteristic polynomial



      $p(lambda)= {rm det}(A − lambda I d)= (lambda + 2)^2 (1 − λ)$



      So from here I know that one of the root is 1 and the other one is -2. However, it states on the answer sheet that the multiplicity of -2 is 2 ? How come ? I don't see two -2 roots in the equation .



      Somebody please help?







      matrices matrix-equations matrix-calculus diagonalization






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      share|cite|improve this question













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      edited Nov 30 '18 at 19:08









      David G. Stork

      10.2k21332




      10.2k21332










      asked Nov 30 '18 at 18:57









      BM97BM97

      758




      758






















          1 Answer
          1






          active

          oldest

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          0












          $begingroup$

          Think of your characteristic equation as:



          $$p(lambda) = (lambda + 2)(lambda + 2)(1 - lambda)$$



          to see the multiplicity of eigenvalues better.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So i would need to look at (λ + 2)² as it if were two distinct equations?
            $endgroup$
            – BM97
            Nov 30 '18 at 19:02










          • $begingroup$
            No... having two (equal) solutions.
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:06










          • $begingroup$
            I don't understand ; i meant i need to see (λ + 2)² as two different brackets as you said
            $endgroup$
            – BM97
            Nov 30 '18 at 19:08










          • $begingroup$
            Are you unfamiliar with the fact that $(lambda + 2)^2 = (lambda +2)(lambda + 2)$?????
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:09











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          1 Answer
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          1 Answer
          1






          active

          oldest

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          active

          oldest

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          active

          oldest

          votes









          0












          $begingroup$

          Think of your characteristic equation as:



          $$p(lambda) = (lambda + 2)(lambda + 2)(1 - lambda)$$



          to see the multiplicity of eigenvalues better.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So i would need to look at (λ + 2)² as it if were two distinct equations?
            $endgroup$
            – BM97
            Nov 30 '18 at 19:02










          • $begingroup$
            No... having two (equal) solutions.
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:06










          • $begingroup$
            I don't understand ; i meant i need to see (λ + 2)² as two different brackets as you said
            $endgroup$
            – BM97
            Nov 30 '18 at 19:08










          • $begingroup$
            Are you unfamiliar with the fact that $(lambda + 2)^2 = (lambda +2)(lambda + 2)$?????
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:09
















          0












          $begingroup$

          Think of your characteristic equation as:



          $$p(lambda) = (lambda + 2)(lambda + 2)(1 - lambda)$$



          to see the multiplicity of eigenvalues better.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So i would need to look at (λ + 2)² as it if were two distinct equations?
            $endgroup$
            – BM97
            Nov 30 '18 at 19:02










          • $begingroup$
            No... having two (equal) solutions.
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:06










          • $begingroup$
            I don't understand ; i meant i need to see (λ + 2)² as two different brackets as you said
            $endgroup$
            – BM97
            Nov 30 '18 at 19:08










          • $begingroup$
            Are you unfamiliar with the fact that $(lambda + 2)^2 = (lambda +2)(lambda + 2)$?????
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:09














          0












          0








          0





          $begingroup$

          Think of your characteristic equation as:



          $$p(lambda) = (lambda + 2)(lambda + 2)(1 - lambda)$$



          to see the multiplicity of eigenvalues better.






          share|cite|improve this answer









          $endgroup$



          Think of your characteristic equation as:



          $$p(lambda) = (lambda + 2)(lambda + 2)(1 - lambda)$$



          to see the multiplicity of eigenvalues better.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Nov 30 '18 at 19:01









          David G. StorkDavid G. Stork

          10.2k21332




          10.2k21332












          • $begingroup$
            So i would need to look at (λ + 2)² as it if were two distinct equations?
            $endgroup$
            – BM97
            Nov 30 '18 at 19:02










          • $begingroup$
            No... having two (equal) solutions.
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:06










          • $begingroup$
            I don't understand ; i meant i need to see (λ + 2)² as two different brackets as you said
            $endgroup$
            – BM97
            Nov 30 '18 at 19:08










          • $begingroup$
            Are you unfamiliar with the fact that $(lambda + 2)^2 = (lambda +2)(lambda + 2)$?????
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:09


















          • $begingroup$
            So i would need to look at (λ + 2)² as it if were two distinct equations?
            $endgroup$
            – BM97
            Nov 30 '18 at 19:02










          • $begingroup$
            No... having two (equal) solutions.
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:06










          • $begingroup$
            I don't understand ; i meant i need to see (λ + 2)² as two different brackets as you said
            $endgroup$
            – BM97
            Nov 30 '18 at 19:08










          • $begingroup$
            Are you unfamiliar with the fact that $(lambda + 2)^2 = (lambda +2)(lambda + 2)$?????
            $endgroup$
            – David G. Stork
            Nov 30 '18 at 19:09
















          $begingroup$
          So i would need to look at (λ + 2)² as it if were two distinct equations?
          $endgroup$
          – BM97
          Nov 30 '18 at 19:02




          $begingroup$
          So i would need to look at (λ + 2)² as it if were two distinct equations?
          $endgroup$
          – BM97
          Nov 30 '18 at 19:02












          $begingroup$
          No... having two (equal) solutions.
          $endgroup$
          – David G. Stork
          Nov 30 '18 at 19:06




          $begingroup$
          No... having two (equal) solutions.
          $endgroup$
          – David G. Stork
          Nov 30 '18 at 19:06












          $begingroup$
          I don't understand ; i meant i need to see (λ + 2)² as two different brackets as you said
          $endgroup$
          – BM97
          Nov 30 '18 at 19:08




          $begingroup$
          I don't understand ; i meant i need to see (λ + 2)² as two different brackets as you said
          $endgroup$
          – BM97
          Nov 30 '18 at 19:08












          $begingroup$
          Are you unfamiliar with the fact that $(lambda + 2)^2 = (lambda +2)(lambda + 2)$?????
          $endgroup$
          – David G. Stork
          Nov 30 '18 at 19:09




          $begingroup$
          Are you unfamiliar with the fact that $(lambda + 2)^2 = (lambda +2)(lambda + 2)$?????
          $endgroup$
          – David G. Stork
          Nov 30 '18 at 19:09


















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