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Homework Help: Finding Inverse of a Transformation

  1. Mar 11, 2012 #1
    1. The problem statement, all variables and given/known data


    3. The attempt at a solution
    Suppose we take an arbitrary polynomial in [itex]P_2 (R)[/itex], call this [itex]a_0 + a_1 x + a_2 x^2[/itex]

    [itex]T(a_0 + a_1 x + a_2 x^2) = (a_0, a_0 + a_1 + a_2, a_0 - a_1 + a_2)[/itex]

    Now, I was under the impression that I could construct a matrix for T by showing what T does to each of the standard basis vectors of [itex]P_2 (R)[/itex], these being the set [itex]1,x,x^2[/itex].

    Doing some mapping: [itex]T(1 + 0x + 0x^2) = (1,1,1), T(0 + 1x + 0x^2) = (0,1,-1), T(0+0x+1x^2) = (0,1,1)[/itex].

    Thus my matrix for T has these outputs as its columns. Via some elementary row reduction I concluded that the matrix (with semicolons indicating the end of a row) [1 0 0;0 1/2 1/2;-1 1/2 -1/2] is the inverse of T, call it S.

    Moreover, it can be checked that T*S = I, which leads me to suspect that I have the write answer. Does this look about right?
  2. jcsd
  3. Mar 11, 2012 #2
    Yes it does
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