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Homework Help: Linear algebra problem involving image spaces

  1. Oct 1, 2012 #1
    1. The problem statement, all variables and given/known data
    A is a mxn. V is nxn and invertible. Show that imA=imAV

    2. The attempt at a solution
    Up until now I haven't done much in the way of proving things. In this case is it enough to show that they are each closed under addition and scalar multiplication? Would that mean that imA is in imAV and vice versa, meaning they are equal?

    Thanks for any help
    Last edited: Oct 1, 2012
  2. jcsd
  3. Oct 1, 2012 #2


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    Science Advisor

    Since A is "m by n", A maps Rn to Rm. Since V is "n by n", V maps Rn to Rn[/b] so that AV maps Rn to Rm.

    Suppose w is in Im(A). Then there exist v in Rn such that Av= w. Since V is invertible, there exist u in Rn such that Vu= v. Then (AV)u= A(Vu)= A(v)= w. That is Im(AV) is a subset of Im(V). To prove that Im(AV)= Im(A), you must prove that Im(A) is a subset of Im(AV). To do that start "suppose w is in Im(AV). I will leave it to you.
  4. Oct 1, 2012 #3
    I see where you are going with that. Does that mean that everything I did was wrong? I thought that if I proved they were subspaces of each other that would mean they are equal
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