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Dot product with 2 variables

  1. Jun 2, 2016 #1
    1. The problem statement, all variables and given/known data
    This problem actually has 2 parts.
    For vectors a= (2,p,8) and b= (q,4,12), determine the values of p and q so that the vectors are a)perpendicular b) collinear

    textbook answer: a) p= 1 and q= -50 (answers may vary) b) p= 8/3 and q=3

    2. Relevant equations
    a*b = 0

    a*b = a1b1 + a2b2 + a3b3

    3. The attempt at a solution

    So for the first part, I used a*b = 0 and I don't know how to do the second part

    a*b = 0
    (2,p,8)*(q,4,12) = 0
    2q + 4p + 96 =0

    I tried isolating p and q and substituting them but I end up with 0.
  2. jcsd
  3. Jun 2, 2016 #2


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    First part: What do you mean by "end up with zero"? You are supposed to pick p and q so that the inner product is zero.

    Second part: What does it mean for two vectors to be collinear?
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