Problem related to linear transformation

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Problem



Assume that a linear transformation $T$ has two eigenvectors $x$ and $y$ belonging to two distinct eigenvalue
$lambda$ and $mu$ . If $ax+by$ is an eigenvector of$T$,prove that $a=0$ or $b=0$.



Attempt



$T(x)=lambda x$ and $T(y) = mu y$.
$T(ax+by) = omega(ax+by)$,where $omega$ is an eigenvalue for $ax+by$.



$a(lambda -omega)=0$ and $b(mu-omega) =0$ since $x$ and$ y$ are independent( distinct eigenvalues)
.



Problem



How to arrive at result after that ?







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  • show that if $a$ is not zero then $b=0$
    – Lozenges
    Sep 1 at 6:36














up vote
2
down vote

favorite












Problem



Assume that a linear transformation $T$ has two eigenvectors $x$ and $y$ belonging to two distinct eigenvalue
$lambda$ and $mu$ . If $ax+by$ is an eigenvector of$T$,prove that $a=0$ or $b=0$.



Attempt



$T(x)=lambda x$ and $T(y) = mu y$.
$T(ax+by) = omega(ax+by)$,where $omega$ is an eigenvalue for $ax+by$.



$a(lambda -omega)=0$ and $b(mu-omega) =0$ since $x$ and$ y$ are independent( distinct eigenvalues)
.



Problem



How to arrive at result after that ?







share|cite|improve this question




















  • show that if $a$ is not zero then $b=0$
    – Lozenges
    Sep 1 at 6:36












up vote
2
down vote

favorite









up vote
2
down vote

favorite











Problem



Assume that a linear transformation $T$ has two eigenvectors $x$ and $y$ belonging to two distinct eigenvalue
$lambda$ and $mu$ . If $ax+by$ is an eigenvector of$T$,prove that $a=0$ or $b=0$.



Attempt



$T(x)=lambda x$ and $T(y) = mu y$.
$T(ax+by) = omega(ax+by)$,where $omega$ is an eigenvalue for $ax+by$.



$a(lambda -omega)=0$ and $b(mu-omega) =0$ since $x$ and$ y$ are independent( distinct eigenvalues)
.



Problem



How to arrive at result after that ?







share|cite|improve this question












Problem



Assume that a linear transformation $T$ has two eigenvectors $x$ and $y$ belonging to two distinct eigenvalue
$lambda$ and $mu$ . If $ax+by$ is an eigenvector of$T$,prove that $a=0$ or $b=0$.



Attempt



$T(x)=lambda x$ and $T(y) = mu y$.
$T(ax+by) = omega(ax+by)$,where $omega$ is an eigenvalue for $ax+by$.



$a(lambda -omega)=0$ and $b(mu-omega) =0$ since $x$ and$ y$ are independent( distinct eigenvalues)
.



Problem



How to arrive at result after that ?









share|cite|improve this question











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asked Sep 1 at 6:16









blue boy

1,085513




1,085513











  • show that if $a$ is not zero then $b=0$
    – Lozenges
    Sep 1 at 6:36
















  • show that if $a$ is not zero then $b=0$
    – Lozenges
    Sep 1 at 6:36















show that if $a$ is not zero then $b=0$
– Lozenges
Sep 1 at 6:36




show that if $a$ is not zero then $b=0$
– Lozenges
Sep 1 at 6:36










2 Answers
2






active

oldest

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up vote
3
down vote



accepted











$T(ax+by) = omega(ax+by)$, where $omega$ is an eigenvalue for $ax+by$.




As noted, by linearity $,omega(ax+by) = T(ax+by) = a T(x) + bT(y) = alambda x + b mu y,$, and by linear independence $,a lambda = a omega,$ and $,bmu = b omega,$. Multiplying the first equality by $b$ and the second one by $a$ then subtracting gives $requirecancel,balambda-abmu=baomega-abomega=0 iff ab(lambda-mu)=0,$, and since $,lambda ne mu;ldots$






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    Your approach is correct. Now that $lambda ne mu$, there can be no $omega$ that simultaneously satisfies both the equations (assuming a and b are not equal to zero). So the possible solutions are,



    • a or b = 0 and $omega$ taking the appropriate value to satisfy the other equation.


    • a, b both are 0, which means the vector becomes a 0 vector and its a trivial case.


    So if ax+by is an eigenvector of T, then either a=0 or b=0.






    share|cite|improve this 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
      3
      down vote



      accepted











      $T(ax+by) = omega(ax+by)$, where $omega$ is an eigenvalue for $ax+by$.




      As noted, by linearity $,omega(ax+by) = T(ax+by) = a T(x) + bT(y) = alambda x + b mu y,$, and by linear independence $,a lambda = a omega,$ and $,bmu = b omega,$. Multiplying the first equality by $b$ and the second one by $a$ then subtracting gives $requirecancel,balambda-abmu=baomega-abomega=0 iff ab(lambda-mu)=0,$, and since $,lambda ne mu;ldots$






      share|cite|improve this answer
























        up vote
        3
        down vote



        accepted











        $T(ax+by) = omega(ax+by)$, where $omega$ is an eigenvalue for $ax+by$.




        As noted, by linearity $,omega(ax+by) = T(ax+by) = a T(x) + bT(y) = alambda x + b mu y,$, and by linear independence $,a lambda = a omega,$ and $,bmu = b omega,$. Multiplying the first equality by $b$ and the second one by $a$ then subtracting gives $requirecancel,balambda-abmu=baomega-abomega=0 iff ab(lambda-mu)=0,$, and since $,lambda ne mu;ldots$






        share|cite|improve this answer






















          up vote
          3
          down vote



          accepted







          up vote
          3
          down vote



          accepted







          $T(ax+by) = omega(ax+by)$, where $omega$ is an eigenvalue for $ax+by$.




          As noted, by linearity $,omega(ax+by) = T(ax+by) = a T(x) + bT(y) = alambda x + b mu y,$, and by linear independence $,a lambda = a omega,$ and $,bmu = b omega,$. Multiplying the first equality by $b$ and the second one by $a$ then subtracting gives $requirecancel,balambda-abmu=baomega-abomega=0 iff ab(lambda-mu)=0,$, and since $,lambda ne mu;ldots$






          share|cite|improve this answer













          $T(ax+by) = omega(ax+by)$, where $omega$ is an eigenvalue for $ax+by$.




          As noted, by linearity $,omega(ax+by) = T(ax+by) = a T(x) + bT(y) = alambda x + b mu y,$, and by linear independence $,a lambda = a omega,$ and $,bmu = b omega,$. Multiplying the first equality by $b$ and the second one by $a$ then subtracting gives $requirecancel,balambda-abmu=baomega-abomega=0 iff ab(lambda-mu)=0,$, and since $,lambda ne mu;ldots$







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Sep 1 at 6:42









          dxiv

          55.9k64798




          55.9k64798




















              up vote
              2
              down vote













              Your approach is correct. Now that $lambda ne mu$, there can be no $omega$ that simultaneously satisfies both the equations (assuming a and b are not equal to zero). So the possible solutions are,



              • a or b = 0 and $omega$ taking the appropriate value to satisfy the other equation.


              • a, b both are 0, which means the vector becomes a 0 vector and its a trivial case.


              So if ax+by is an eigenvector of T, then either a=0 or b=0.






              share|cite|improve this answer
























                up vote
                2
                down vote













                Your approach is correct. Now that $lambda ne mu$, there can be no $omega$ that simultaneously satisfies both the equations (assuming a and b are not equal to zero). So the possible solutions are,



                • a or b = 0 and $omega$ taking the appropriate value to satisfy the other equation.


                • a, b both are 0, which means the vector becomes a 0 vector and its a trivial case.


                So if ax+by is an eigenvector of T, then either a=0 or b=0.






                share|cite|improve this answer






















                  up vote
                  2
                  down vote










                  up vote
                  2
                  down vote









                  Your approach is correct. Now that $lambda ne mu$, there can be no $omega$ that simultaneously satisfies both the equations (assuming a and b are not equal to zero). So the possible solutions are,



                  • a or b = 0 and $omega$ taking the appropriate value to satisfy the other equation.


                  • a, b both are 0, which means the vector becomes a 0 vector and its a trivial case.


                  So if ax+by is an eigenvector of T, then either a=0 or b=0.






                  share|cite|improve this answer












                  Your approach is correct. Now that $lambda ne mu$, there can be no $omega$ that simultaneously satisfies both the equations (assuming a and b are not equal to zero). So the possible solutions are,



                  • a or b = 0 and $omega$ taking the appropriate value to satisfy the other equation.


                  • a, b both are 0, which means the vector becomes a 0 vector and its a trivial case.


                  So if ax+by is an eigenvector of T, then either a=0 or b=0.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered Sep 1 at 6:37









                  Lokesh Kumar

                  1363




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