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Math Help - Vector help!

  1. #1
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    Vector help!

    Alright, so I have two questions actually on the same subject. The first is:

    The figure shows a vector a in the xy-plane and a vector b in the direction of k. Their lengths arc |a|=3 and |b|=2. Find |a x b|.

    I know the equation is |a x b| = |a||b|sin(theta) but I can't figure out how to find theta. I've looked up solutions for the problem and people keep saying pi/2. I just don't know how they are coming up with this!!! Help?


    The second is:

    Show that (a x b) dotted with b = 0 for all vectors a and b in Vsub3.

    I'm not good at the math symbols so yeah. Sorry it's not really easy to read but I can't figure out what exactly to do for this. I'm not too good with proving something. Any help appreciated!


    Thanks,
    Cen
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  2. #2
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    Quote Originally Posted by Centara View Post
    The figure shows a vector a in the xy-plane and a vector b in the direction of k. Their lengths arc |a|=3 and |b|=2. Find |a x b|.
    The vector k is perpendicular to any line which is a subset of the xy-plane.
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  3. #3
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    Thank you!

    Any advice on the second one?
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  4. #4
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    Quote Originally Posted by Centara View Post
    Any advice on the second one?
    By definition a \times b is a vector that is perpendicular to both a & b.
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