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Math Help - Unit Vectors - M1

  1. #1
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    Unit Vectors - M1

    I don't really know if this belongs here, but I couldn't find anwhere to put it. All help appreciated.

    Given that vector a = i - 2j and vector b = -3i + j find:

    a) p, if 'a + xb' is parallel to -i - 3j
    b) q, if 'qa + b' is parallel to 2i + j

    Answers: a) 1/2
    b) 1

    I am looking for some help and working. Advanced thanks.
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  2. #2
    Junior Member
    Joined
    May 2008
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    2 vectors v=v_1i+v_2j,w=w_1i+w_2j are parallel iff \frac{v_1}{w_1}=\frac{v_2}{w_2}. After computing a+pb we get (1-3p)i+(p-2)j and with the condition of parallelism we have that \frac{1-3p}{-1}=\frac{p-2}{-3}, from where we have p=\frac{1}{2}, for a).
    For b), is the same thing, try to solve yourself.
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