dimension and basis of a solution space based on the rank of a matrix and three vectors












1












$begingroup$


I am new to linear algebra and have been wrestling with the following question for hours. I have no teacher, and the answer book provides no key. Can anyone suggest a way to go about this?



Let $Ainmathbb{R}^{ 4times4}$, with rank $2$.
Suppose that the vectors
$u=(2,1,2,0),, v=(1,-1,2,4),, w=(1,0,2,-1)$
are solutions to the linear system $Ax=b$.



a. find the dimension of the solution space of the system $Ax=0$ and find its basis.



b. find the general solution to the system $Ax=b$.



Thank you very much










share|cite|improve this question











$endgroup$

















    1












    $begingroup$


    I am new to linear algebra and have been wrestling with the following question for hours. I have no teacher, and the answer book provides no key. Can anyone suggest a way to go about this?



    Let $Ainmathbb{R}^{ 4times4}$, with rank $2$.
    Suppose that the vectors
    $u=(2,1,2,0),, v=(1,-1,2,4),, w=(1,0,2,-1)$
    are solutions to the linear system $Ax=b$.



    a. find the dimension of the solution space of the system $Ax=0$ and find its basis.



    b. find the general solution to the system $Ax=b$.



    Thank you very much










    share|cite|improve this question











    $endgroup$















      1












      1








      1





      $begingroup$


      I am new to linear algebra and have been wrestling with the following question for hours. I have no teacher, and the answer book provides no key. Can anyone suggest a way to go about this?



      Let $Ainmathbb{R}^{ 4times4}$, with rank $2$.
      Suppose that the vectors
      $u=(2,1,2,0),, v=(1,-1,2,4),, w=(1,0,2,-1)$
      are solutions to the linear system $Ax=b$.



      a. find the dimension of the solution space of the system $Ax=0$ and find its basis.



      b. find the general solution to the system $Ax=b$.



      Thank you very much










      share|cite|improve this question











      $endgroup$




      I am new to linear algebra and have been wrestling with the following question for hours. I have no teacher, and the answer book provides no key. Can anyone suggest a way to go about this?



      Let $Ainmathbb{R}^{ 4times4}$, with rank $2$.
      Suppose that the vectors
      $u=(2,1,2,0),, v=(1,-1,2,4),, w=(1,0,2,-1)$
      are solutions to the linear system $Ax=b$.



      a. find the dimension of the solution space of the system $Ax=0$ and find its basis.



      b. find the general solution to the system $Ax=b$.



      Thank you very much







      linear-algebra






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Dec 22 '18 at 19:55









      Martín Vacas Vignolo

      3,816623




      3,816623










      asked Dec 22 '18 at 19:51









      daltadalta

      1238




      1238






















          1 Answer
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          $begingroup$

          $A$ is a matrix of rank $2$ which means that it has a $2$ dimensional kernel. Since $u,v,w$ have the same image, $u-v$ and $u-w$ are in the kernel. Since these two vectors are linearly independent, they span the kernel.



          To get all solutions of $Ax=b$, you can take any solution and translate it with kernel elements, i.e every solution of the equation is of the form $u+c(u-v)+d(u-w)$ where $c,dinmathbb{R}$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So the solution space is an affine linear space!
            $endgroup$
            – Mustang
            Dec 22 '18 at 20:57






          • 1




            $begingroup$
            Yes, it is. This is in general true. For a matrix $A$ and a vector $b$ in the image of $A$, the solutions of $Ax=b$ are always given by $u+N(A)$ where $u$ is a solution of the equation and $N(A)$ is the kernel of $A$.
            $endgroup$
            – Levent
            Dec 22 '18 at 20:58













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          active

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          2












          $begingroup$

          $A$ is a matrix of rank $2$ which means that it has a $2$ dimensional kernel. Since $u,v,w$ have the same image, $u-v$ and $u-w$ are in the kernel. Since these two vectors are linearly independent, they span the kernel.



          To get all solutions of $Ax=b$, you can take any solution and translate it with kernel elements, i.e every solution of the equation is of the form $u+c(u-v)+d(u-w)$ where $c,dinmathbb{R}$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So the solution space is an affine linear space!
            $endgroup$
            – Mustang
            Dec 22 '18 at 20:57






          • 1




            $begingroup$
            Yes, it is. This is in general true. For a matrix $A$ and a vector $b$ in the image of $A$, the solutions of $Ax=b$ are always given by $u+N(A)$ where $u$ is a solution of the equation and $N(A)$ is the kernel of $A$.
            $endgroup$
            – Levent
            Dec 22 '18 at 20:58


















          2












          $begingroup$

          $A$ is a matrix of rank $2$ which means that it has a $2$ dimensional kernel. Since $u,v,w$ have the same image, $u-v$ and $u-w$ are in the kernel. Since these two vectors are linearly independent, they span the kernel.



          To get all solutions of $Ax=b$, you can take any solution and translate it with kernel elements, i.e every solution of the equation is of the form $u+c(u-v)+d(u-w)$ where $c,dinmathbb{R}$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So the solution space is an affine linear space!
            $endgroup$
            – Mustang
            Dec 22 '18 at 20:57






          • 1




            $begingroup$
            Yes, it is. This is in general true. For a matrix $A$ and a vector $b$ in the image of $A$, the solutions of $Ax=b$ are always given by $u+N(A)$ where $u$ is a solution of the equation and $N(A)$ is the kernel of $A$.
            $endgroup$
            – Levent
            Dec 22 '18 at 20:58
















          2












          2








          2





          $begingroup$

          $A$ is a matrix of rank $2$ which means that it has a $2$ dimensional kernel. Since $u,v,w$ have the same image, $u-v$ and $u-w$ are in the kernel. Since these two vectors are linearly independent, they span the kernel.



          To get all solutions of $Ax=b$, you can take any solution and translate it with kernel elements, i.e every solution of the equation is of the form $u+c(u-v)+d(u-w)$ where $c,dinmathbb{R}$.






          share|cite|improve this answer









          $endgroup$



          $A$ is a matrix of rank $2$ which means that it has a $2$ dimensional kernel. Since $u,v,w$ have the same image, $u-v$ and $u-w$ are in the kernel. Since these two vectors are linearly independent, they span the kernel.



          To get all solutions of $Ax=b$, you can take any solution and translate it with kernel elements, i.e every solution of the equation is of the form $u+c(u-v)+d(u-w)$ where $c,dinmathbb{R}$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Dec 22 '18 at 20:37









          LeventLevent

          2,729925




          2,729925












          • $begingroup$
            So the solution space is an affine linear space!
            $endgroup$
            – Mustang
            Dec 22 '18 at 20:57






          • 1




            $begingroup$
            Yes, it is. This is in general true. For a matrix $A$ and a vector $b$ in the image of $A$, the solutions of $Ax=b$ are always given by $u+N(A)$ where $u$ is a solution of the equation and $N(A)$ is the kernel of $A$.
            $endgroup$
            – Levent
            Dec 22 '18 at 20:58




















          • $begingroup$
            So the solution space is an affine linear space!
            $endgroup$
            – Mustang
            Dec 22 '18 at 20:57






          • 1




            $begingroup$
            Yes, it is. This is in general true. For a matrix $A$ and a vector $b$ in the image of $A$, the solutions of $Ax=b$ are always given by $u+N(A)$ where $u$ is a solution of the equation and $N(A)$ is the kernel of $A$.
            $endgroup$
            – Levent
            Dec 22 '18 at 20:58


















          $begingroup$
          So the solution space is an affine linear space!
          $endgroup$
          – Mustang
          Dec 22 '18 at 20:57




          $begingroup$
          So the solution space is an affine linear space!
          $endgroup$
          – Mustang
          Dec 22 '18 at 20:57




          1




          1




          $begingroup$
          Yes, it is. This is in general true. For a matrix $A$ and a vector $b$ in the image of $A$, the solutions of $Ax=b$ are always given by $u+N(A)$ where $u$ is a solution of the equation and $N(A)$ is the kernel of $A$.
          $endgroup$
          – Levent
          Dec 22 '18 at 20:58






          $begingroup$
          Yes, it is. This is in general true. For a matrix $A$ and a vector $b$ in the image of $A$, the solutions of $Ax=b$ are always given by $u+N(A)$ where $u$ is a solution of the equation and $N(A)$ is the kernel of $A$.
          $endgroup$
          – Levent
          Dec 22 '18 at 20:58




















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