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Math Help - What is the standard definition of transforms T_{1,-1} and D_2

  1. #1
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    What is the standard definition of transforms T_{1,-1} and D_2

    What is the standard definitions of the following transforms? I got them from a practice test for the NY Regents. The test does not include those definitions in its reference sheet.

    1. T_{1,-1}
    2. D_2


    I need this for the following:
    Triangle ABC has vertices A(5,1), B(1,4), and C(1,1). What are the coordinates of triangle A''B''C'', the image of triangle ABC following composite transformation T_{1,-1} \circ D_2.

    Answer: A''(11,1), B''(3,7), and C''(3,1).
    Thanks.
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  2. #2
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    Re: What is the standard definition of transforms T_{1,-1} and D_2

    I'd say the NY regents need a copy editor. However, my initial guess was T_{a,b} is translation by (a,b):
    T_{a,b}\> (x,y)=(x+a,y+b).
    Next guess was D_k is central dilation by k about the origin:
    D_k(x,y)=(kx,ky)

    Apparently, from the answer, my guesses were "correct". Guessing games have no place in a math test.
    Thanks from emakarov and ILikeSerena
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  3. #3
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    Re: What is the standard definition of transforms T_{1,-1} and D_2

    Agree on the copy editor and guessing remark. The sample test was off of their website, so it was probably an official past test.
    Last edited by mathDad; March 18th 2013 at 11:25 AM.
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