Q&A #6308

Teachers' Lounge Discussion: Vector orientation

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From: redwan

To: Teacher2Teacher Public Discussion
Date: 2007032504:51:20
Subject: Re: Re: Vectors - dot.product and cross product

On 2007021814:32:34, Loyd wrote:
>On 2001062117:39:50, John Oke wrote:
>>I have a lot of difficulty in understanding the meaning and
>>computation of dot.products and cross products. My other problem is
>>being able to state the angle between a line and a plane. Is it
>>possible to explain these in easy terms/words for an average
>>I shall be verygrateful	
>There is a wealth of information on dot and cross product on the web.

>I too, have always wanted a better understanding of these two vector
>operations.  Go to Google and search for "Cross Product."  Lots of
>I have a TI-89 and this calculator has cross product built in and it
>also has dot product (I have to use magnifying glass to see TI-89
>screen).  In fact just the other day, I happened to look at a Cliff
>Notes book for linear algebra and saw cross product explained and
>brought back college days memories when I was first exposed to what I
>though was very abstract.   I happened to look in my TI-89 book and
>saw that it could do cross product.  
>Then a few days later, I talked to a pre med student at a major
>university who was also having some difficulty with cross product.  I
>mentioned that the TI-89 could do this operation.  The student was
>surprised because they used that model in class.  
>After reading your post, I looked on Google and searched for cross
>product with TI -89 and came up with this at:

>"Determining cross products and dot products by hand:
>P x Q = (1i + 2j + 3k) x (5i + 0j - 1k)
>= 5(i x i) + 0(i x j) - 1(i x k) +10(j x i) + 0(j x j) - 2(j x k) +
>15(k x i) + 0(k x j) - 3(k x k)
>= 5(0) + 0(k) - 1(-j) + 10(-k) + 0(0) - 2(i) + 15(j) + 0(-i) - 3(0)
>= -2i + 16j - 10k
>= (-2,16,-10)
>P  Q = (1i + 2j + 3k)  (5i + 0j - 1k) = (1)(5) + (2)(0) + (3)(-1) =
>5 + 0 - 3 = 2"
>That is the first time that I have seen this hand method.  The
>is easy to follow.  On the TI 89, I went to Math, Vector ops, cross
>product and did this:
>crossP( [ 1, 2, 3 ] , [ 5, 0, -1 ] ) enter and the answer comes up.
>The above PDF paper says use catalog.  I didn't try that.  One web
>site said use the TI-89 for homework if need be, but it was not
>allowed on exams.  Too easy! 
>The cross product has application in electicity and magnetisim.  In
>the early days electricity and magnetisim were separate fields and
>Oersted discovered in a class that if a compass is parrallel to a
>with current flow,  the needle would swing to a right angle position.

>Thus, electricity and magnetisim were related.  I have also seen
>product used in mechanics courses.  

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