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Math Help - Linear Algebra Special Matrices Problem!

  1. #1
    Junior Member
    Joined
    May 2007
    Posts
    34

    Linear Algebra Special Matrices Problem!

    What 2 by 2 matrix P projects the vector (x,y) onto the x axis to produce (x,0)?
    What matrix Q projects onto the y axis to produce (0,y)?
    If you multiply (5,7) by P and then multiply by Q, you get (_____) and (_____). (Fill in the vector-blanks)
    *the vectors in part three arent neccessarily 5 dimensions!)

    I'm pretty sure I found P and Q, but for the third problem I only got 1 vector...

    My answer:
    Q= [
    001
    100
    010]
    P= [
    010
    001
    100]
    P*Q*(5,7)=(0,0)=0 ... And yet the problem asks for two (i'm assuming nonzero) vectors... What have i done wrong?

    (PS Im on my blackberry!)
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  2. #2
    Newbie
    Joined
    Sep 2008
    Posts
    12
    well the matrix to extract the x-coordinate of a vector, i.e. [P] is
    1 0
    0 0

    and [Q] would be
    0 0
    0 1

    I don't know why you got 3x3 matrices when you're only working in a 2x2 space...hopefully it should work out for you now

    also the first answer will be (5,7).P and the second answer will be (5,7).Q (i think anyway)
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