$Av=lambda v Rightarrow A^*v=bar lambda v$ (general case)











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Suppose $V$ is a finite-dimensional complex inner product space and $v_1,v_2,...,v_3$ is an orthonormal basis of $V$.
Define $A:V to V$ by $Av_i=lambda_i v_i$ for some $lambda_i in mathbb{C}.$
Show that $A^*v_i=bar lambda v_i.$



My attempt:



$(Av_i,v_i)=(lambda_iv_i,v_i)=(v_i,barlambda_i v_i)=(v_i,A^*v_i)$



$Rightarrow(v_i,(A^*-bar lambda_i)v_i)=0 Rightarrow (A^*-bar lambda_i)v_i perp v_i $



How to show that $(A^*-barlambda_i)v_i=0$ ?










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    Suppose $V$ is a finite-dimensional complex inner product space and $v_1,v_2,...,v_3$ is an orthonormal basis of $V$.
    Define $A:V to V$ by $Av_i=lambda_i v_i$ for some $lambda_i in mathbb{C}.$
    Show that $A^*v_i=bar lambda v_i.$



    My attempt:



    $(Av_i,v_i)=(lambda_iv_i,v_i)=(v_i,barlambda_i v_i)=(v_i,A^*v_i)$



    $Rightarrow(v_i,(A^*-bar lambda_i)v_i)=0 Rightarrow (A^*-bar lambda_i)v_i perp v_i $



    How to show that $(A^*-barlambda_i)v_i=0$ ?










    share|cite|improve this question


























      up vote
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      up vote
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      favorite
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      3





      Suppose $V$ is a finite-dimensional complex inner product space and $v_1,v_2,...,v_3$ is an orthonormal basis of $V$.
      Define $A:V to V$ by $Av_i=lambda_i v_i$ for some $lambda_i in mathbb{C}.$
      Show that $A^*v_i=bar lambda v_i.$



      My attempt:



      $(Av_i,v_i)=(lambda_iv_i,v_i)=(v_i,barlambda_i v_i)=(v_i,A^*v_i)$



      $Rightarrow(v_i,(A^*-bar lambda_i)v_i)=0 Rightarrow (A^*-bar lambda_i)v_i perp v_i $



      How to show that $(A^*-barlambda_i)v_i=0$ ?










      share|cite|improve this question















      Suppose $V$ is a finite-dimensional complex inner product space and $v_1,v_2,...,v_3$ is an orthonormal basis of $V$.
      Define $A:V to V$ by $Av_i=lambda_i v_i$ for some $lambda_i in mathbb{C}.$
      Show that $A^*v_i=bar lambda v_i.$



      My attempt:



      $(Av_i,v_i)=(lambda_iv_i,v_i)=(v_i,barlambda_i v_i)=(v_i,A^*v_i)$



      $Rightarrow(v_i,(A^*-bar lambda_i)v_i)=0 Rightarrow (A^*-bar lambda_i)v_i perp v_i $



      How to show that $(A^*-barlambda_i)v_i=0$ ?







      linear-algebra matrices adjoint-operators






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      edited Nov 16 at 14:38

























      asked Nov 16 at 14:21









      XYZ

      1858




      1858






















          2 Answers
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          Just extend what you have a bit:
          begin{align}
          langle sum_j a_j v_j,A^*sum_k b_k v_k rangle = &langle A sum_{j}a_j v_j, sum_{k}b_k v_krangle \
          = & langle sum_{j}lambda_j a_j v_j,sum_k b_k v_krangle \
          = &sum_jlambda_j a_joverline{b_j} \
          = &langlesum_j a_j v_j,sum_k overline{lambda_k}b_kv_krangle \
          end{align}






          share|cite|improve this answer























          • @user1561 : Like the way I have redone it?
            – DisintegratingByParts
            Nov 16 at 17:01






          • 1




            Yes. $phantom{}$+1.
            – user1551
            Nov 16 at 17:23


















          up vote
          0
          down vote













          Here is another method:



          Let $M=[A]_beta$, where $beta={v_i}_{1le ile n}$. Then $det,(M-lambda I)=0impliesdet,(M-lambda I)^*=0$.






          share|cite|improve this answer























            Your Answer





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            2 Answers
            2






            active

            oldest

            votes








            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes








            up vote
            2
            down vote













            Just extend what you have a bit:
            begin{align}
            langle sum_j a_j v_j,A^*sum_k b_k v_k rangle = &langle A sum_{j}a_j v_j, sum_{k}b_k v_krangle \
            = & langle sum_{j}lambda_j a_j v_j,sum_k b_k v_krangle \
            = &sum_jlambda_j a_joverline{b_j} \
            = &langlesum_j a_j v_j,sum_k overline{lambda_k}b_kv_krangle \
            end{align}






            share|cite|improve this answer























            • @user1561 : Like the way I have redone it?
              – DisintegratingByParts
              Nov 16 at 17:01






            • 1




              Yes. $phantom{}$+1.
              – user1551
              Nov 16 at 17:23















            up vote
            2
            down vote













            Just extend what you have a bit:
            begin{align}
            langle sum_j a_j v_j,A^*sum_k b_k v_k rangle = &langle A sum_{j}a_j v_j, sum_{k}b_k v_krangle \
            = & langle sum_{j}lambda_j a_j v_j,sum_k b_k v_krangle \
            = &sum_jlambda_j a_joverline{b_j} \
            = &langlesum_j a_j v_j,sum_k overline{lambda_k}b_kv_krangle \
            end{align}






            share|cite|improve this answer























            • @user1561 : Like the way I have redone it?
              – DisintegratingByParts
              Nov 16 at 17:01






            • 1




              Yes. $phantom{}$+1.
              – user1551
              Nov 16 at 17:23













            up vote
            2
            down vote










            up vote
            2
            down vote









            Just extend what you have a bit:
            begin{align}
            langle sum_j a_j v_j,A^*sum_k b_k v_k rangle = &langle A sum_{j}a_j v_j, sum_{k}b_k v_krangle \
            = & langle sum_{j}lambda_j a_j v_j,sum_k b_k v_krangle \
            = &sum_jlambda_j a_joverline{b_j} \
            = &langlesum_j a_j v_j,sum_k overline{lambda_k}b_kv_krangle \
            end{align}






            share|cite|improve this answer














            Just extend what you have a bit:
            begin{align}
            langle sum_j a_j v_j,A^*sum_k b_k v_k rangle = &langle A sum_{j}a_j v_j, sum_{k}b_k v_krangle \
            = & langle sum_{j}lambda_j a_j v_j,sum_k b_k v_krangle \
            = &sum_jlambda_j a_joverline{b_j} \
            = &langlesum_j a_j v_j,sum_k overline{lambda_k}b_kv_krangle \
            end{align}







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            edited Nov 16 at 17:00

























            answered Nov 16 at 15:06









            DisintegratingByParts

            57.9k42477




            57.9k42477












            • @user1561 : Like the way I have redone it?
              – DisintegratingByParts
              Nov 16 at 17:01






            • 1




              Yes. $phantom{}$+1.
              – user1551
              Nov 16 at 17:23


















            • @user1561 : Like the way I have redone it?
              – DisintegratingByParts
              Nov 16 at 17:01






            • 1




              Yes. $phantom{}$+1.
              – user1551
              Nov 16 at 17:23
















            @user1561 : Like the way I have redone it?
            – DisintegratingByParts
            Nov 16 at 17:01




            @user1561 : Like the way I have redone it?
            – DisintegratingByParts
            Nov 16 at 17:01




            1




            1




            Yes. $phantom{}$+1.
            – user1551
            Nov 16 at 17:23




            Yes. $phantom{}$+1.
            – user1551
            Nov 16 at 17:23










            up vote
            0
            down vote













            Here is another method:



            Let $M=[A]_beta$, where $beta={v_i}_{1le ile n}$. Then $det,(M-lambda I)=0impliesdet,(M-lambda I)^*=0$.






            share|cite|improve this answer



























              up vote
              0
              down vote













              Here is another method:



              Let $M=[A]_beta$, where $beta={v_i}_{1le ile n}$. Then $det,(M-lambda I)=0impliesdet,(M-lambda I)^*=0$.






              share|cite|improve this answer

























                up vote
                0
                down vote










                up vote
                0
                down vote









                Here is another method:



                Let $M=[A]_beta$, where $beta={v_i}_{1le ile n}$. Then $det,(M-lambda I)=0impliesdet,(M-lambda I)^*=0$.






                share|cite|improve this answer














                Here is another method:



                Let $M=[A]_beta$, where $beta={v_i}_{1le ile n}$. Then $det,(M-lambda I)=0impliesdet,(M-lambda I)^*=0$.







                share|cite|improve this answer














                share|cite|improve this answer



                share|cite|improve this answer








                edited Nov 16 at 16:00

























                answered Nov 16 at 15:07









                614177

                416




                416






























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