Results 1 to 5 of 5

Math Help - proof

  1. #1
    Newbie
    Joined
    Oct 2008
    Posts
    14

    Exclamation proof

    Couuld someone please help me with the following proofs:

    (iii) If
    u × v = v × u then we must have u × v = 0.

    (iv) If
    u is a vector such that u × v = 0 for every vector v, then we must have u = 0.

    Need Help urgent please.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by maths_123 View Post
    Couuld someone please help me with the following proofs:

    (iii) If
    [LEFT]u × v = v × u then we must have u × v = 0.

    hint: note that the cross-product is anti-commutative. so in general, u x v = -v x u

    (iv) If
    u is a vector such that u × v = 0 for every vector v, then we must have u = 0.
    Need Help urgent please.
    i guess you could do this using the formula. the other thing i had in mind might not work. let \bold{u} = \left< u_1,u_2,u_3 \right> and \bold{v} = \left< v_1,v_2,v_3 \right>

    then \bold{u} \times \bold{v} = \cdots = 0

    show that you must have u_1 = u_2 = u_3 = 0
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Oct 2008
    Posts
    14
    I don't understand how u x v = -v x u is linked with

    u × v = v × u then we must have u × v = 0.


    And what forumal should i use?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by maths_123 View Post
    I don't understand how u x v = -v x u is linked with

    u × v = v × u then we must have u × v = 0.


    And what forumal should i use?
    think about it

    u x v = -v x u

    and

    u x v = v x u

    .
    .
    .
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Oct 2008
    Posts
    14
    Quote Originally Posted by Jhevon View Post
    think about it

    u x v = -v x u

    and

    u x v = v x u

    .
    .
    .
    Thanks for the help, i was ablr to solve thw question after all
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: October 19th 2010, 10:50 AM
  2. Replies: 0
    Last Post: June 29th 2010, 08:48 AM
  3. [SOLVED] direct proof and proof by contradiction
    Posted in the Number Theory Forum
    Replies: 2
    Last Post: February 27th 2010, 10:07 PM
  4. Proof with algebra, and proof by induction (problems)
    Posted in the Discrete Math Forum
    Replies: 8
    Last Post: June 8th 2008, 01:20 PM
  5. proof that the proof that .999_ = 1 is not a proof (version)
    Posted in the Advanced Applied Math Forum
    Replies: 4
    Last Post: April 14th 2008, 04:07 PM

Search Tags


/mathhelpforum @mathhelpforum