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Homework Help: Help with part of my Linear Algebras project - affine sets and mappings

  1. Mar 6, 2012 #1
    1. The problem statement, all variables and given/known data
    I'm a 2nd year undergraduate student, so I suppose many users here won't find this too difficult, but I've had some issues with the following questions and, of course, any help would be very much appreciated:

    (i) Prove f: V→W is affine (where V and W are real vector space) iff it is of the form f(x) = Tx + b, where T: V→ W is linear and b∈W. Prove T and b are uniquely determined by f.

    (ii) Prove the image of an affine subset under an affine mapping is affine. Prove the composition of two affine maps is affine.

    2. Relevant equations

    3. The attempt at a solution

    (i) If f: V→W is an affine mapping, we must have f(λx + (1-λ)y) = λf(x) + (1-λ)f(y) for all x and y in V, and λ in ℝ.
    This is what immediately came to mind, but I can't see a connection between this and the question...

    (ii) I'm sorry, but I've gone over this again and again and don't know where to start.

  2. jcsd
  3. Mar 6, 2012 #2


    User Avatar
    Science Advisor

    Try substituting the condition on 3i) into f(x) in 1i), and see if it is satisfied. I think it may help you over the

    long run if you have a good feel for the meaning of an Affine map. Not that you should

    drop rigor at all, but it helps if you understand what is going on at an informal level.

    Basically, to start, an affine map is a translation/shift of a linear map.
  4. Mar 12, 2012 #3
    This thread has been closed because of academic misconduct.
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