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Dot product

  1. Mar 15, 2013 #1
    find 2 unit vectors that make an angle of pi/3 with <3,4>

    b=5/8-3/4 a

    such that
    a^2+25/64+15/16a+9/16 a^2=1
    25/16 a^2+15/16/ a=39/64
    so far so good

    =(17-6sqrt(3))/20 // correct me if im wrong
  2. jcsd
  3. Mar 16, 2013 #2


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    hi nameVoid! :smile:

    your method looks basically correct (but i haven't checked it)

    however, it's really complicated

    try first finding the vector perpendicular to (3,4) and with the same magnitude :wink:
  4. Mar 16, 2013 #3
    The solution for b2 is incorrect by the book
  5. Mar 16, 2013 #4


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    shouldn't it be minus 15/16 ? :wink:
  6. Mar 19, 2013 #5
    Ah yes my mistake
  7. Mar 20, 2013 #6


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    Looking at <3, 4>, you should have seen that <4, -3> is perpendicular without needing to write anything!
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