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Find the cross product of the following vectors. Then use the cross product to find the angle between them.

 a = 3i − 2j + 5k and b = 7i + 4j − 8k

Guest Jun 14, 2014

Best Answer 

 #1
avatar+26412 
+8

crossproduct

Alan  Jun 14, 2014
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9+0 Answers

 #1
avatar+26412 
+8
Best Answer

crossproduct

Alan  Jun 14, 2014
 #2
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0

sorry, im a little confused. did you just turn a and b into and v? 

Guest Jun 14, 2014
 #3
avatar+26412 
+5

I used u and v as general vectors.  a and b are your specific vectors.  That is they are specific examples of u and v.  But if you prefer to think of it as turning a and b into u and v ok!  Whatever works for you!

 

In fact, why don't you rewrite my u and v in terms of a and b (including their components - so u1 becomes a1 etc.)?

Alan  Jun 14, 2014
 #4
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thanks for the help

Guest Jun 14, 2014
 #5
avatar+26412 
0

You're welcome.

Alan  Jun 14, 2014
 #6
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sorry, think i did something wrong..my a × b= -4,11,4. 

so i'll call it y. y= a3 b1 - a1 b3. 

a = 3 − 2 + 5 and b = 7 + 4 − 8

 

y=(5)(7)-(3)(8)
 = 35-24
 =11


I noticed however you got 59..where did i go wrong? 

Guest Jun 14, 2014
 #7
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0

nevermind. i figured it out. two negatives is a positive. Thanks again for the help. 

Guest Jun 14, 2014
 #8
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i have a new issue now.

p = −2i − 3j and q =4i +7j. (Note: these vectors are 3D).

Does that mean there HAS to be a third? 

Guest Jun 14, 2014
 #9
avatar+26412 
+5

Yes, there has to be a third component; but it is zero!

So p = −2i − 3j + 0k and q =4i +7j + 0k.  It measn p and q are both in the i,j plane; and their cross-product will be in the k direction. 

Alan  Jun 15, 2014

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