Prove that linear operator T is the projection Operator












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I got question prove or disprove




Let be $T:mathbb R^n to mathbb R^n$ linear oprator and let be $Usubsetmathbb R^n$ hyperplane.


If known that $Image(T)=U$ and also that for every $uin U$, $T(u)=u$.



So $T$ is projection operator on $U$.




Thank you for the help :)










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    0












    $begingroup$


    I got question prove or disprove




    Let be $T:mathbb R^n to mathbb R^n$ linear oprator and let be $Usubsetmathbb R^n$ hyperplane.


    If known that $Image(T)=U$ and also that for every $uin U$, $T(u)=u$.



    So $T$ is projection operator on $U$.




    Thank you for the help :)










    share|cite|improve this question











    $endgroup$















      0












      0








      0





      $begingroup$


      I got question prove or disprove




      Let be $T:mathbb R^n to mathbb R^n$ linear oprator and let be $Usubsetmathbb R^n$ hyperplane.


      If known that $Image(T)=U$ and also that for every $uin U$, $T(u)=u$.



      So $T$ is projection operator on $U$.




      Thank you for the help :)










      share|cite|improve this question











      $endgroup$




      I got question prove or disprove




      Let be $T:mathbb R^n to mathbb R^n$ linear oprator and let be $Usubsetmathbb R^n$ hyperplane.


      If known that $Image(T)=U$ and also that for every $uin U$, $T(u)=u$.



      So $T$ is projection operator on $U$.




      Thank you for the help :)







      linear-transformations projection






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      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Jan 26 at 14:11









      Mundron Schmidt

      7,5042729




      7,5042729










      asked Jan 26 at 14:06









      Or Yehuda Ben ShimolOr Yehuda Ben Shimol

      132




      132






















          1 Answer
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          0












          $begingroup$

          I assume, the projection operator is defined as $T^2=T$.



          Consider $vin mathbb R^n$. Can you think of a way, why $T^2v=Tv$ holds? It is maybe easier to see if you write
          $$
          T^2v=Tv Leftrightarrow T(T(v)) = T(v).
          $$

          You don't to it normally this way, but let us make it one step more obvious:



          We define $w=Tv$. Now we get
          $$
          T(T(v))=T(v) Leftrightarrow T(w)=w.
          $$

          Consider, that $w$ is an element of the image of $T$.
          And that this holds, is writen in your condition.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            I didn't understand, can you give me an example maybe ?
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 15:43












          • $begingroup$
            I rewrote it a bit. But the step to see, why $T^2=T$ holds if $T$ is the identity on its image, which is a hyperplane, is a very small one... It isn't even worth to be called a proof.
            $endgroup$
            – Mundron Schmidt
            Jan 26 at 16:10










          • $begingroup$
            Thank you very much !!!
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 19:13











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          1 Answer
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          1 Answer
          1






          active

          oldest

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          active

          oldest

          votes









          0












          $begingroup$

          I assume, the projection operator is defined as $T^2=T$.



          Consider $vin mathbb R^n$. Can you think of a way, why $T^2v=Tv$ holds? It is maybe easier to see if you write
          $$
          T^2v=Tv Leftrightarrow T(T(v)) = T(v).
          $$

          You don't to it normally this way, but let us make it one step more obvious:



          We define $w=Tv$. Now we get
          $$
          T(T(v))=T(v) Leftrightarrow T(w)=w.
          $$

          Consider, that $w$ is an element of the image of $T$.
          And that this holds, is writen in your condition.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            I didn't understand, can you give me an example maybe ?
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 15:43












          • $begingroup$
            I rewrote it a bit. But the step to see, why $T^2=T$ holds if $T$ is the identity on its image, which is a hyperplane, is a very small one... It isn't even worth to be called a proof.
            $endgroup$
            – Mundron Schmidt
            Jan 26 at 16:10










          • $begingroup$
            Thank you very much !!!
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 19:13
















          0












          $begingroup$

          I assume, the projection operator is defined as $T^2=T$.



          Consider $vin mathbb R^n$. Can you think of a way, why $T^2v=Tv$ holds? It is maybe easier to see if you write
          $$
          T^2v=Tv Leftrightarrow T(T(v)) = T(v).
          $$

          You don't to it normally this way, but let us make it one step more obvious:



          We define $w=Tv$. Now we get
          $$
          T(T(v))=T(v) Leftrightarrow T(w)=w.
          $$

          Consider, that $w$ is an element of the image of $T$.
          And that this holds, is writen in your condition.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            I didn't understand, can you give me an example maybe ?
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 15:43












          • $begingroup$
            I rewrote it a bit. But the step to see, why $T^2=T$ holds if $T$ is the identity on its image, which is a hyperplane, is a very small one... It isn't even worth to be called a proof.
            $endgroup$
            – Mundron Schmidt
            Jan 26 at 16:10










          • $begingroup$
            Thank you very much !!!
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 19:13














          0












          0








          0





          $begingroup$

          I assume, the projection operator is defined as $T^2=T$.



          Consider $vin mathbb R^n$. Can you think of a way, why $T^2v=Tv$ holds? It is maybe easier to see if you write
          $$
          T^2v=Tv Leftrightarrow T(T(v)) = T(v).
          $$

          You don't to it normally this way, but let us make it one step more obvious:



          We define $w=Tv$. Now we get
          $$
          T(T(v))=T(v) Leftrightarrow T(w)=w.
          $$

          Consider, that $w$ is an element of the image of $T$.
          And that this holds, is writen in your condition.






          share|cite|improve this answer











          $endgroup$



          I assume, the projection operator is defined as $T^2=T$.



          Consider $vin mathbb R^n$. Can you think of a way, why $T^2v=Tv$ holds? It is maybe easier to see if you write
          $$
          T^2v=Tv Leftrightarrow T(T(v)) = T(v).
          $$

          You don't to it normally this way, but let us make it one step more obvious:



          We define $w=Tv$. Now we get
          $$
          T(T(v))=T(v) Leftrightarrow T(w)=w.
          $$

          Consider, that $w$ is an element of the image of $T$.
          And that this holds, is writen in your condition.







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited Jan 26 at 16:08

























          answered Jan 26 at 14:15









          Mundron SchmidtMundron Schmidt

          7,5042729




          7,5042729












          • $begingroup$
            I didn't understand, can you give me an example maybe ?
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 15:43












          • $begingroup$
            I rewrote it a bit. But the step to see, why $T^2=T$ holds if $T$ is the identity on its image, which is a hyperplane, is a very small one... It isn't even worth to be called a proof.
            $endgroup$
            – Mundron Schmidt
            Jan 26 at 16:10










          • $begingroup$
            Thank you very much !!!
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 19:13


















          • $begingroup$
            I didn't understand, can you give me an example maybe ?
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 15:43












          • $begingroup$
            I rewrote it a bit. But the step to see, why $T^2=T$ holds if $T$ is the identity on its image, which is a hyperplane, is a very small one... It isn't even worth to be called a proof.
            $endgroup$
            – Mundron Schmidt
            Jan 26 at 16:10










          • $begingroup$
            Thank you very much !!!
            $endgroup$
            – Or Yehuda Ben Shimol
            Jan 26 at 19:13
















          $begingroup$
          I didn't understand, can you give me an example maybe ?
          $endgroup$
          – Or Yehuda Ben Shimol
          Jan 26 at 15:43






          $begingroup$
          I didn't understand, can you give me an example maybe ?
          $endgroup$
          – Or Yehuda Ben Shimol
          Jan 26 at 15:43














          $begingroup$
          I rewrote it a bit. But the step to see, why $T^2=T$ holds if $T$ is the identity on its image, which is a hyperplane, is a very small one... It isn't even worth to be called a proof.
          $endgroup$
          – Mundron Schmidt
          Jan 26 at 16:10




          $begingroup$
          I rewrote it a bit. But the step to see, why $T^2=T$ holds if $T$ is the identity on its image, which is a hyperplane, is a very small one... It isn't even worth to be called a proof.
          $endgroup$
          – Mundron Schmidt
          Jan 26 at 16:10












          $begingroup$
          Thank you very much !!!
          $endgroup$
          – Or Yehuda Ben Shimol
          Jan 26 at 19:13




          $begingroup$
          Thank you very much !!!
          $endgroup$
          – Or Yehuda Ben Shimol
          Jan 26 at 19:13


















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