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Homework Help: Triple Scalar Product

  1. Feb 3, 2007 #1
    1. The problem statement, all variables and given/known data
    What is the value of a(dot)(a(cross)b) ? Why?
    I am supposed to find an actual value.
    Sorry I dont know code, these variables are all vectors. A is dotted with vectors a and b which are cross product.
    2. Relevant equations
    I know this can be written as a determinate of all three variables but I do not see how this gives me a single answer.

    3. The attempt at a solution
  2. jcsd
  3. Feb 3, 2007 #2


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    axb is perpendicular to a and b. The relevant part of this is that it is perpendicular to a, so axb is some vector c perpendicular to a. So what is a.c when c is perpendicular to a?
  4. Feb 4, 2007 #3
    Try this, write out the cross product by hand.

    Once you have the cross product, take the scalar product.

    (There is a trick to this question, see if you can find it).
  5. Feb 4, 2007 #4


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    ^ ^physicist, you're evil! Yes, once CaityAnn has gone through that pain, perhaps she will learn that it is better to think!
  6. Feb 4, 2007 #5
    It may be evil, but I find if you work through it this way, after doing it a couple of times you start seeing the trick...
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