Triple Scalar Product

  • Thread starter CaityAnn
  • Start date
  • #1
CaityAnn
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Homework Statement


What is the value of a(dot)(a(cross)b) ? Why?
I am supposed to find an actual value.
Sorry I don't know code, these variables are all vectors. A is dotted with vectors a and b which are cross product.

Homework 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.


The Attempt at a Solution

 

Answers and Replies

  • #2
AKG
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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?
 
  • #3
^_^physicist
235
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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).
 
  • #4
HallsofIvy
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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!
 
  • #5
^_^physicist
235
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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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