Question about Image and Kernel in a combined Linear Transformation












0












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I am new to Linear Algebra, and was asked the following question:




Let $S,T:Vto V$ be linear transformations, while V is a linear space.



If $mbox{im} ST={0}$ then $mbox{im} Tsubseteq ker S$




I have tried to reason this through, but I am not sure whether my reasoning is correct:



$$ker S: Sunderline x=0$$



$$mbox{im} T = text{ column-space of }T$$



So if I multiply $S times T$, with the result being ${0}$, that would seem to imply that indeed $T$ is a subset of $ker S$, as it obeys $Sunderline x=0$, with $T$ taking the place of $underline x$.



Can anybody help out?



Thank you










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  • $begingroup$
    Shouldn't it be the composition of linear maps $S$ and $T$ rather than mentioning it as multiplication? @dalta
    $endgroup$
    – toric_actions
    Jan 1 at 16:17
















0












$begingroup$


I am new to Linear Algebra, and was asked the following question:




Let $S,T:Vto V$ be linear transformations, while V is a linear space.



If $mbox{im} ST={0}$ then $mbox{im} Tsubseteq ker S$




I have tried to reason this through, but I am not sure whether my reasoning is correct:



$$ker S: Sunderline x=0$$



$$mbox{im} T = text{ column-space of }T$$



So if I multiply $S times T$, with the result being ${0}$, that would seem to imply that indeed $T$ is a subset of $ker S$, as it obeys $Sunderline x=0$, with $T$ taking the place of $underline x$.



Can anybody help out?



Thank you










share|cite|improve this question











$endgroup$












  • $begingroup$
    Shouldn't it be the composition of linear maps $S$ and $T$ rather than mentioning it as multiplication? @dalta
    $endgroup$
    – toric_actions
    Jan 1 at 16:17














0












0








0





$begingroup$


I am new to Linear Algebra, and was asked the following question:




Let $S,T:Vto V$ be linear transformations, while V is a linear space.



If $mbox{im} ST={0}$ then $mbox{im} Tsubseteq ker S$




I have tried to reason this through, but I am not sure whether my reasoning is correct:



$$ker S: Sunderline x=0$$



$$mbox{im} T = text{ column-space of }T$$



So if I multiply $S times T$, with the result being ${0}$, that would seem to imply that indeed $T$ is a subset of $ker S$, as it obeys $Sunderline x=0$, with $T$ taking the place of $underline x$.



Can anybody help out?



Thank you










share|cite|improve this question











$endgroup$




I am new to Linear Algebra, and was asked the following question:




Let $S,T:Vto V$ be linear transformations, while V is a linear space.



If $mbox{im} ST={0}$ then $mbox{im} Tsubseteq ker S$




I have tried to reason this through, but I am not sure whether my reasoning is correct:



$$ker S: Sunderline x=0$$



$$mbox{im} T = text{ column-space of }T$$



So if I multiply $S times T$, with the result being ${0}$, that would seem to imply that indeed $T$ is a subset of $ker S$, as it obeys $Sunderline x=0$, with $T$ taking the place of $underline x$.



Can anybody help out?



Thank you







linear-algebra linear-transformations






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edited Jan 1 at 16:44









amWhy

192k28225439




192k28225439










asked Jan 1 at 16:04









daltadalta

627




627












  • $begingroup$
    Shouldn't it be the composition of linear maps $S$ and $T$ rather than mentioning it as multiplication? @dalta
    $endgroup$
    – toric_actions
    Jan 1 at 16:17


















  • $begingroup$
    Shouldn't it be the composition of linear maps $S$ and $T$ rather than mentioning it as multiplication? @dalta
    $endgroup$
    – toric_actions
    Jan 1 at 16:17
















$begingroup$
Shouldn't it be the composition of linear maps $S$ and $T$ rather than mentioning it as multiplication? @dalta
$endgroup$
– toric_actions
Jan 1 at 16:17




$begingroup$
Shouldn't it be the composition of linear maps $S$ and $T$ rather than mentioning it as multiplication? @dalta
$endgroup$
– toric_actions
Jan 1 at 16:17










1 Answer
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$begingroup$

I think you have the right idea - let's just be slightly more precise.



Suppose $y in textrm{Im}(T)$, so $y = T(x)$ for some $x in V$. Then $S(y) = ST(x) = 0$ since $ST = 0$ and hence $y in textrm{Ker}(S)$. Therefore $textrm{Im}(T) subseteq textrm{Ker}(S)$.






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    1 Answer
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    1 Answer
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    $begingroup$

    I think you have the right idea - let's just be slightly more precise.



    Suppose $y in textrm{Im}(T)$, so $y = T(x)$ for some $x in V$. Then $S(y) = ST(x) = 0$ since $ST = 0$ and hence $y in textrm{Ker}(S)$. Therefore $textrm{Im}(T) subseteq textrm{Ker}(S)$.






    share|cite|improve this answer









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      1












      $begingroup$

      I think you have the right idea - let's just be slightly more precise.



      Suppose $y in textrm{Im}(T)$, so $y = T(x)$ for some $x in V$. Then $S(y) = ST(x) = 0$ since $ST = 0$ and hence $y in textrm{Ker}(S)$. Therefore $textrm{Im}(T) subseteq textrm{Ker}(S)$.






      share|cite|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        I think you have the right idea - let's just be slightly more precise.



        Suppose $y in textrm{Im}(T)$, so $y = T(x)$ for some $x in V$. Then $S(y) = ST(x) = 0$ since $ST = 0$ and hence $y in textrm{Ker}(S)$. Therefore $textrm{Im}(T) subseteq textrm{Ker}(S)$.






        share|cite|improve this answer









        $endgroup$



        I think you have the right idea - let's just be slightly more precise.



        Suppose $y in textrm{Im}(T)$, so $y = T(x)$ for some $x in V$. Then $S(y) = ST(x) = 0$ since $ST = 0$ and hence $y in textrm{Ker}(S)$. Therefore $textrm{Im}(T) subseteq textrm{Ker}(S)$.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 1 at 16:11









        ODFODF

        1,396510




        1,396510






























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