Results 1 to 8 of 8

Math Help - How do I start this vector problem

  1. #1
    Junior Member
    Joined
    Mar 2008
    Posts
    37

    How do I start this vector problem

    and , find a unit vector with positive first coordinate orthogonal to both and .

    I can do the calculation myself, i'm just not sure where to start
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by Allie View Post
    and , find a unit vector with positive first coordinate orthogonal to both and .

    I can do the calculation myself, i'm just not sure where to start
    Start by taking the cross product of a and b.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Mar 2008
    Posts
    37
    I did do that is there another step? I seem to be missing omething
    for the dot product i get
    (10i+j+20k)-(20i+j-10k) which would give me -10i+10k. I know the j coefficient is 0 but where did i go wrong with the others?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by Allie View Post
    I did do that is there another step? I seem to be missing omething
    for the dot product i get
    (10i+j+20k)-(20i+j-10k) which would give me -10i+10k. I know the j coefficient is 0 but where did i go wrong with the others?
    I said cross product, not dot product.

    Are you aware there are two different way of multiplying two vectors? Have you been taught how to take the cross product of two vectors?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Mar 2008
    Posts
    37
    yes im aware and i did the cross product i don't know why i said dot.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by Allie View Post
    yes im aware and i did the cross product i don't know why i said dot.
    So -10i+10k is perpendicular to a and b. Obviously any scalar multiple of -10i+10k is also perpendicular. So 10i - 10k is perpendicular (and satisfies the requirement of the i-component being positive).

    Do you know how to get a unit vector in the direction of 10i - 10k ?
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    Mar 2008
    Posts
    37
    yes you have to divide it through by the magnitude thank you
    Last edited by Allie; September 6th 2008 at 06:22 PM.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by Allie View Post
    no
    You know how to do a cross product but can't construct a unit vector!?

    Divide 10i - 10k by its magnitude.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] How do I start this problem?
    Posted in the Calculus Forum
    Replies: 8
    Last Post: October 17th 2010, 02:08 AM
  2. algebra problem where to start
    Posted in the Algebra Forum
    Replies: 1
    Last Post: November 30th 2009, 09:59 AM
  3. How do I start this problem?
    Posted in the Calculus Forum
    Replies: 2
    Last Post: September 16th 2009, 08:59 PM
  4. Where do I start this triq problem?
    Posted in the Trigonometry Forum
    Replies: 12
    Last Post: June 17th 2008, 07:28 PM
  5. how to start this limit problem....
    Posted in the Calculus Forum
    Replies: 2
    Last Post: May 18th 2008, 11:05 PM

Search Tags


/mathhelpforum @mathhelpforum