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Homework Help: Basis of image of linear transformation

  1. Apr 20, 2008 #1
    1. The problem statement, all variables and given/known data
    Find a basis of the image im(LA) of the linear transformation

    LA: R^5 [tex]\rightarrow[/tex]R^3, x[tex]\mapsto[/tex]Ax


    A =
    1 -2 2 3 -1
    -3 6 -1 1 -7
    2 -4 5 8 -4

    and hence determine the dimension of im(LA)

    3. The attempt at a solution
    Using the equation LA= Ax,

    can i set up an augmented matrix of A and say, y1, y2 and y3 on the end? Then perform row reduction to get it into row reduced echelon form. Is that the right way to go about it? I will perform the calculation and update with it but any direction would be greatly appreciated.
  2. jcsd
  3. Apr 20, 2008 #2
    A has row reduced form of:

    1 -2 0 -1 3 y1-2y3
    0 0 1 2 -2 y3-2y1
    0 0 0 0 0 y2-3y1-5y3

    I have the solutions to the basis of the null space for A, how is this case different?
  4. Apr 20, 2008 #3
    I rearranged the equations to get:


    Does this even have any use, im just getting lost with this thing. Please help, urgent.
  5. Apr 21, 2008 #4


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    That is not what I get! You had to divide by 5 to get that "1" in the second row didn't you? In the last column, I get, for the second row, (y3- 2y1)/5 and, for the third row (5y3- 13y1-y2)/5. In order that there exist x such that Ax= y you must have 5y3- 13y1- y2= 0. That is the same as y2= 5y3- 13y1 so if you take y1= 1, y3= 0, y2 must be -13. <1, -13, 0> is in the image. If you take y1= 0, y3= 1, y2 must be 5. <0, 5, 1> is in the image.
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