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Math Help - dot/cross product rules

  1. #1
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    dot/cross product rules

    Just asking for some tips for answering questions, such as:
    1)Find a such that i-4k is perpendicular to the vector -3i + ak
    2)Suppose x and y are vectors which are linearly independent and the following vector equation holds for some scalars a and b: 9x + a(x+y) = b(x-2y). Find a and b.
    3)Suppose x and y are vectors which are linearly independent and the following vector equation holds for some scalars a and b: -4x + a(x+y) = b(x-3y). Find a and b.

    Thanks for any help
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  2. #2
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    Re: dot/cross product rules

    i) Two vectors are perpendicular when their dot product is 0.

    ii) Expand, collect like terms, and equate the coefficients of x and the coefficients of y.

    iii) See ii).
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