Show that if $T$ is surjective and spans $V$, then $T(S)$ spans $W$. Announcing the arrival of...

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Show that if $T$ is surjective and spans $V$, then $T(S)$ spans $W$.



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)How to show that a linear map is surjective?Soft question: Why freshmen feel linear algebra is abstract?How to show a set spans a space?Invariant subspace - simplified definitionDifferences between finding linear independence and finding a spanning set.Linear independence, Spanning, Injectivity, and SurjectivityCompleteness, spanning and orthonormal basesBuilding a surjective functionSpanning set definition and theoremShow that $textrm{trace}: textrm{End}(V)rightarrow k$ defined by $textrm{trace}(phi ):=textrm{trace}(M(phi ))$ is a linear map.












2












$begingroup$



Given that $T: V to W$ is a linear transformation from $V$ to $W$. Show that if $T$ is surjective and $Ssubset V$ spans $V$, then $T(S)$ spans $W$.




I think the main thing stumping me right now is how to use spanning to show anything or what I would need to prove in order to show that $W$ has been successfully spanned. I understand how to use the definition of linear transformation and surjective, but I can't even get started (OR CAN I???) without a clear understanding of how spanning works.



I understand span in concrete numbers, so I need help getting a more abstract concept of $operatorname{span} (S)$, if possible. And I tried YouTube and reading definitions already, I am truly stuck.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    How would a linear map span a subspace? What is S in all this?
    $endgroup$
    – Bernard
    Jan 22 '17 at 1:59










  • $begingroup$
    What is $S$? It seems to have just shown up out of nowhere in this question.
    $endgroup$
    – The Count
    Jan 22 '17 at 1:59










  • $begingroup$
    I've edited your question. Please check that this is what you meant.
    $endgroup$
    – user378947
    Jan 22 '17 at 2:02






  • 1




    $begingroup$
    Yes, thank you for editing, that better says what I was trying to say.
    $endgroup$
    – Snackbreak
    Jan 22 '17 at 5:01
















2












$begingroup$



Given that $T: V to W$ is a linear transformation from $V$ to $W$. Show that if $T$ is surjective and $Ssubset V$ spans $V$, then $T(S)$ spans $W$.




I think the main thing stumping me right now is how to use spanning to show anything or what I would need to prove in order to show that $W$ has been successfully spanned. I understand how to use the definition of linear transformation and surjective, but I can't even get started (OR CAN I???) without a clear understanding of how spanning works.



I understand span in concrete numbers, so I need help getting a more abstract concept of $operatorname{span} (S)$, if possible. And I tried YouTube and reading definitions already, I am truly stuck.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    How would a linear map span a subspace? What is S in all this?
    $endgroup$
    – Bernard
    Jan 22 '17 at 1:59










  • $begingroup$
    What is $S$? It seems to have just shown up out of nowhere in this question.
    $endgroup$
    – The Count
    Jan 22 '17 at 1:59










  • $begingroup$
    I've edited your question. Please check that this is what you meant.
    $endgroup$
    – user378947
    Jan 22 '17 at 2:02






  • 1




    $begingroup$
    Yes, thank you for editing, that better says what I was trying to say.
    $endgroup$
    – Snackbreak
    Jan 22 '17 at 5:01














2












2








2





$begingroup$



Given that $T: V to W$ is a linear transformation from $V$ to $W$. Show that if $T$ is surjective and $Ssubset V$ spans $V$, then $T(S)$ spans $W$.




I think the main thing stumping me right now is how to use spanning to show anything or what I would need to prove in order to show that $W$ has been successfully spanned. I understand how to use the definition of linear transformation and surjective, but I can't even get started (OR CAN I???) without a clear understanding of how spanning works.



I understand span in concrete numbers, so I need help getting a more abstract concept of $operatorname{span} (S)$, if possible. And I tried YouTube and reading definitions already, I am truly stuck.










share|cite|improve this question











$endgroup$





Given that $T: V to W$ is a linear transformation from $V$ to $W$. Show that if $T$ is surjective and $Ssubset V$ spans $V$, then $T(S)$ spans $W$.




I think the main thing stumping me right now is how to use spanning to show anything or what I would need to prove in order to show that $W$ has been successfully spanned. I understand how to use the definition of linear transformation and surjective, but I can't even get started (OR CAN I???) without a clear understanding of how spanning works.



I understand span in concrete numbers, so I need help getting a more abstract concept of $operatorname{span} (S)$, if possible. And I tried YouTube and reading definitions already, I am truly stuck.







linear-algebra linear-transformations transformation






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 23 at 22:05









Rócherz

3,0263823




3,0263823










asked Jan 22 '17 at 1:54









SnackbreakSnackbreak

314




314








  • 1




    $begingroup$
    How would a linear map span a subspace? What is S in all this?
    $endgroup$
    – Bernard
    Jan 22 '17 at 1:59










  • $begingroup$
    What is $S$? It seems to have just shown up out of nowhere in this question.
    $endgroup$
    – The Count
    Jan 22 '17 at 1:59










  • $begingroup$
    I've edited your question. Please check that this is what you meant.
    $endgroup$
    – user378947
    Jan 22 '17 at 2:02






  • 1




    $begingroup$
    Yes, thank you for editing, that better says what I was trying to say.
    $endgroup$
    – Snackbreak
    Jan 22 '17 at 5:01














  • 1




    $begingroup$
    How would a linear map span a subspace? What is S in all this?
    $endgroup$
    – Bernard
    Jan 22 '17 at 1:59










  • $begingroup$
    What is $S$? It seems to have just shown up out of nowhere in this question.
    $endgroup$
    – The Count
    Jan 22 '17 at 1:59










  • $begingroup$
    I've edited your question. Please check that this is what you meant.
    $endgroup$
    – user378947
    Jan 22 '17 at 2:02






  • 1




    $begingroup$
    Yes, thank you for editing, that better says what I was trying to say.
    $endgroup$
    – Snackbreak
    Jan 22 '17 at 5:01








1




1




$begingroup$
How would a linear map span a subspace? What is S in all this?
$endgroup$
– Bernard
Jan 22 '17 at 1:59




$begingroup$
How would a linear map span a subspace? What is S in all this?
$endgroup$
– Bernard
Jan 22 '17 at 1:59












$begingroup$
What is $S$? It seems to have just shown up out of nowhere in this question.
$endgroup$
– The Count
Jan 22 '17 at 1:59




$begingroup$
What is $S$? It seems to have just shown up out of nowhere in this question.
$endgroup$
– The Count
Jan 22 '17 at 1:59












$begingroup$
I've edited your question. Please check that this is what you meant.
$endgroup$
– user378947
Jan 22 '17 at 2:02




$begingroup$
I've edited your question. Please check that this is what you meant.
$endgroup$
– user378947
Jan 22 '17 at 2:02




1




1




$begingroup$
Yes, thank you for editing, that better says what I was trying to say.
$endgroup$
– Snackbreak
Jan 22 '17 at 5:01




$begingroup$
Yes, thank you for editing, that better says what I was trying to say.
$endgroup$
– Snackbreak
Jan 22 '17 at 5:01










2 Answers
2






active

oldest

votes


















1












$begingroup$

$S$ spans $V$ simply means that every element $v in V$ can be written (not necessarily uniquely) as a finite linear combination of elements of $S$.



so it is required to prove that every element $w in W$ can be written as a finite linear combination of elements of $T(S)$



now, the fact that $T$ is surjective means that any $w in W$ is the image (under the mapping $T$) of some (not necessarily unique) element of $V$. i.e. we can find $u in V$ such that:



$$
w = T(u)
$$



write $u$ as a finite linear combination of elements of $S$:



$$
u = sum_k lambda_k s_k
$$
where the $lambda_k$ are scalars and each $s_k in S$



since the mapping $T$ is linear we have:



$$
w = T(u) = Tbigg(sum_k lambda_k s_k bigg) = sum_k lambda_k T(s_k)
$$
showing that $w$ is a linear combination of elements of $T(S)$ as required.






share|cite|improve this answer









$endgroup$





















    2












    $begingroup$

    Let $win W$. As $T$ is surjective we know that there is some $vin V$ such that $T(v)=w$. We also know that $S$ spans $V$, so there are $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k.$ Applying $T$ to both sides of this equation yields the desired conclusion.






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      By the way, saying that a subset $S$ of a vector space $V$ spans $V$ means that for every $vin V$ there are a finite number of vectors $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k$. In words, that every vector in $V$ can be expressed as a finite linear combination of elements in $S$.
      $endgroup$
      – user378947
      Jan 22 '17 at 2:07








    • 1




      $begingroup$
      Okay, I think the lambdas were throwing me off in the Wikipedia definition, I wasn't sure how to express anything useful with a sum of (λ sub i)(v sub i), but you breaking it down like that helps significantly. Thank you! @ mathbeing @David Holden
      $endgroup$
      – Snackbreak
      Jan 22 '17 at 5:05












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    2 Answers
    2






    active

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    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    1












    $begingroup$

    $S$ spans $V$ simply means that every element $v in V$ can be written (not necessarily uniquely) as a finite linear combination of elements of $S$.



    so it is required to prove that every element $w in W$ can be written as a finite linear combination of elements of $T(S)$



    now, the fact that $T$ is surjective means that any $w in W$ is the image (under the mapping $T$) of some (not necessarily unique) element of $V$. i.e. we can find $u in V$ such that:



    $$
    w = T(u)
    $$



    write $u$ as a finite linear combination of elements of $S$:



    $$
    u = sum_k lambda_k s_k
    $$
    where the $lambda_k$ are scalars and each $s_k in S$



    since the mapping $T$ is linear we have:



    $$
    w = T(u) = Tbigg(sum_k lambda_k s_k bigg) = sum_k lambda_k T(s_k)
    $$
    showing that $w$ is a linear combination of elements of $T(S)$ as required.






    share|cite|improve this answer









    $endgroup$


















      1












      $begingroup$

      $S$ spans $V$ simply means that every element $v in V$ can be written (not necessarily uniquely) as a finite linear combination of elements of $S$.



      so it is required to prove that every element $w in W$ can be written as a finite linear combination of elements of $T(S)$



      now, the fact that $T$ is surjective means that any $w in W$ is the image (under the mapping $T$) of some (not necessarily unique) element of $V$. i.e. we can find $u in V$ such that:



      $$
      w = T(u)
      $$



      write $u$ as a finite linear combination of elements of $S$:



      $$
      u = sum_k lambda_k s_k
      $$
      where the $lambda_k$ are scalars and each $s_k in S$



      since the mapping $T$ is linear we have:



      $$
      w = T(u) = Tbigg(sum_k lambda_k s_k bigg) = sum_k lambda_k T(s_k)
      $$
      showing that $w$ is a linear combination of elements of $T(S)$ as required.






      share|cite|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        $S$ spans $V$ simply means that every element $v in V$ can be written (not necessarily uniquely) as a finite linear combination of elements of $S$.



        so it is required to prove that every element $w in W$ can be written as a finite linear combination of elements of $T(S)$



        now, the fact that $T$ is surjective means that any $w in W$ is the image (under the mapping $T$) of some (not necessarily unique) element of $V$. i.e. we can find $u in V$ such that:



        $$
        w = T(u)
        $$



        write $u$ as a finite linear combination of elements of $S$:



        $$
        u = sum_k lambda_k s_k
        $$
        where the $lambda_k$ are scalars and each $s_k in S$



        since the mapping $T$ is linear we have:



        $$
        w = T(u) = Tbigg(sum_k lambda_k s_k bigg) = sum_k lambda_k T(s_k)
        $$
        showing that $w$ is a linear combination of elements of $T(S)$ as required.






        share|cite|improve this answer









        $endgroup$



        $S$ spans $V$ simply means that every element $v in V$ can be written (not necessarily uniquely) as a finite linear combination of elements of $S$.



        so it is required to prove that every element $w in W$ can be written as a finite linear combination of elements of $T(S)$



        now, the fact that $T$ is surjective means that any $w in W$ is the image (under the mapping $T$) of some (not necessarily unique) element of $V$. i.e. we can find $u in V$ such that:



        $$
        w = T(u)
        $$



        write $u$ as a finite linear combination of elements of $S$:



        $$
        u = sum_k lambda_k s_k
        $$
        where the $lambda_k$ are scalars and each $s_k in S$



        since the mapping $T$ is linear we have:



        $$
        w = T(u) = Tbigg(sum_k lambda_k s_k bigg) = sum_k lambda_k T(s_k)
        $$
        showing that $w$ is a linear combination of elements of $T(S)$ as required.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 22 '17 at 3:53









        David HoldenDavid Holden

        14.9k21226




        14.9k21226























            2












            $begingroup$

            Let $win W$. As $T$ is surjective we know that there is some $vin V$ such that $T(v)=w$. We also know that $S$ spans $V$, so there are $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k.$ Applying $T$ to both sides of this equation yields the desired conclusion.






            share|cite|improve this answer









            $endgroup$













            • $begingroup$
              By the way, saying that a subset $S$ of a vector space $V$ spans $V$ means that for every $vin V$ there are a finite number of vectors $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k$. In words, that every vector in $V$ can be expressed as a finite linear combination of elements in $S$.
              $endgroup$
              – user378947
              Jan 22 '17 at 2:07








            • 1




              $begingroup$
              Okay, I think the lambdas were throwing me off in the Wikipedia definition, I wasn't sure how to express anything useful with a sum of (λ sub i)(v sub i), but you breaking it down like that helps significantly. Thank you! @ mathbeing @David Holden
              $endgroup$
              – Snackbreak
              Jan 22 '17 at 5:05
















            2












            $begingroup$

            Let $win W$. As $T$ is surjective we know that there is some $vin V$ such that $T(v)=w$. We also know that $S$ spans $V$, so there are $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k.$ Applying $T$ to both sides of this equation yields the desired conclusion.






            share|cite|improve this answer









            $endgroup$













            • $begingroup$
              By the way, saying that a subset $S$ of a vector space $V$ spans $V$ means that for every $vin V$ there are a finite number of vectors $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k$. In words, that every vector in $V$ can be expressed as a finite linear combination of elements in $S$.
              $endgroup$
              – user378947
              Jan 22 '17 at 2:07








            • 1




              $begingroup$
              Okay, I think the lambdas were throwing me off in the Wikipedia definition, I wasn't sure how to express anything useful with a sum of (λ sub i)(v sub i), but you breaking it down like that helps significantly. Thank you! @ mathbeing @David Holden
              $endgroup$
              – Snackbreak
              Jan 22 '17 at 5:05














            2












            2








            2





            $begingroup$

            Let $win W$. As $T$ is surjective we know that there is some $vin V$ such that $T(v)=w$. We also know that $S$ spans $V$, so there are $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k.$ Applying $T$ to both sides of this equation yields the desired conclusion.






            share|cite|improve this answer









            $endgroup$



            Let $win W$. As $T$ is surjective we know that there is some $vin V$ such that $T(v)=w$. We also know that $S$ spans $V$, so there are $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k.$ Applying $T$ to both sides of this equation yields the desired conclusion.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered Jan 22 '17 at 2:00







            user378947



















            • $begingroup$
              By the way, saying that a subset $S$ of a vector space $V$ spans $V$ means that for every $vin V$ there are a finite number of vectors $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k$. In words, that every vector in $V$ can be expressed as a finite linear combination of elements in $S$.
              $endgroup$
              – user378947
              Jan 22 '17 at 2:07








            • 1




              $begingroup$
              Okay, I think the lambdas were throwing me off in the Wikipedia definition, I wasn't sure how to express anything useful with a sum of (λ sub i)(v sub i), but you breaking it down like that helps significantly. Thank you! @ mathbeing @David Holden
              $endgroup$
              – Snackbreak
              Jan 22 '17 at 5:05


















            • $begingroup$
              By the way, saying that a subset $S$ of a vector space $V$ spans $V$ means that for every $vin V$ there are a finite number of vectors $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k$. In words, that every vector in $V$ can be expressed as a finite linear combination of elements in $S$.
              $endgroup$
              – user378947
              Jan 22 '17 at 2:07








            • 1




              $begingroup$
              Okay, I think the lambdas were throwing me off in the Wikipedia definition, I wasn't sure how to express anything useful with a sum of (λ sub i)(v sub i), but you breaking it down like that helps significantly. Thank you! @ mathbeing @David Holden
              $endgroup$
              – Snackbreak
              Jan 22 '17 at 5:05
















            $begingroup$
            By the way, saying that a subset $S$ of a vector space $V$ spans $V$ means that for every $vin V$ there are a finite number of vectors $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k$. In words, that every vector in $V$ can be expressed as a finite linear combination of elements in $S$.
            $endgroup$
            – user378947
            Jan 22 '17 at 2:07






            $begingroup$
            By the way, saying that a subset $S$ of a vector space $V$ spans $V$ means that for every $vin V$ there are a finite number of vectors $v_1,...,v_kin S$ and scalars $lambda_1,...,lambda_k$ such that $v=lambda_1v_1+cdots+lambda_kv_k$. In words, that every vector in $V$ can be expressed as a finite linear combination of elements in $S$.
            $endgroup$
            – user378947
            Jan 22 '17 at 2:07






            1




            1




            $begingroup$
            Okay, I think the lambdas were throwing me off in the Wikipedia definition, I wasn't sure how to express anything useful with a sum of (λ sub i)(v sub i), but you breaking it down like that helps significantly. Thank you! @ mathbeing @David Holden
            $endgroup$
            – Snackbreak
            Jan 22 '17 at 5:05




            $begingroup$
            Okay, I think the lambdas were throwing me off in the Wikipedia definition, I wasn't sure how to express anything useful with a sum of (λ sub i)(v sub i), but you breaking it down like that helps significantly. Thank you! @ mathbeing @David Holden
            $endgroup$
            – Snackbreak
            Jan 22 '17 at 5:05


















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