Results 1 to 5 of 5

Math Help - Vector help please.

  1. #1
    Member
    Joined
    May 2008
    Posts
    150
    Awards
    1

    Vector help please.

    I think its simple...i think i just have a brain block lol...mayb cuz its 12 at night.
    OABC is a rectangle.
    A has position vector (2, -3, 5) (with respect to origin O)
    B has position vector (x, 3, 7)(with respect to origin O)
    Answer x = 6.

    So i thought, these must be perpendicular! Scale product...well...i got s = 13 which is wrong .

    But also if these are perpendicular...won't they share the same x-coordinate? Or Y co-ordinate?

    Cheers in advanced for any help you can give me .
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,610
    Thanks
    1576
    Awards
    1
    Rectangles have right alngles.
    So \overrightarrow {OA} \cdot \overrightarrow {AB} = 0.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Banned
    Joined
    Nov 2008
    Posts
    82
    Quote Originally Posted by AshleyT View Post
    I think its simple...i think i just have a brain block lol...mayb cuz its 12 at night.
    OABC is a rectangle.

    Answer x = 6.

    So i thought, these must be perpendicular! Scale product...well...i got s = 13 which is wrong .

    But also if these are perpendicular...won't they share the same x-coordinate? Or Y co-ordinate?

    Cheers in advanced for any help you can give me .
    hey mate,
    As stated by Plato <OA,AB> = 0 as the shape is rectangular, have you been using <OA,OB> instead?
    either way to solve AB, use AB = B - A

    This will yield the correct solution,

    Regards,

    David
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Nov 2008
    From
    Germany
    Posts
    8
    Hi,

    IŽd like to add an explanation why the vectors do not need to share a co-ordinate to be perpendicular.

    Just look at the attached image.

    Regards,

    Andreas
    Attached Thumbnails Attached Thumbnails Vector help please.-rectangle.png  
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    May 2008
    Posts
    150
    Awards
    1
    Aww, thank-you everyone for your help. I really appreciate it.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 8
    Last Post: January 11th 2011, 10:17 AM
  2. Replies: 2
    Last Post: January 27th 2010, 08:23 PM
  3. Replies: 11
    Last Post: December 23rd 2009, 01:30 AM
  4. Replies: 4
    Last Post: November 5th 2009, 04:03 PM
  5. Replies: 2
    Last Post: October 5th 2009, 03:25 PM

Search Tags


/mathhelpforum @mathhelpforum