Results 1 to 3 of 3

Math Help - Dot product problem

  1. #1
    Newbie
    Joined
    May 2010
    Posts
    2

    Dot product problem

    Ok heres the question i am stuck on. I have tried many things and can't get it.

    The points P(-2,1),Q(-6,4),and R(4,3) are three vertices of parrallelogram PQRS
    a) Find the coordinates of S
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member AllanCuz's Avatar
    Joined
    Apr 2010
    From
    Canada
    Posts
    384
    Thanks
    4
    Quote Originally Posted by canadasbest View Post
    Ok heres the question i am stuck on. I have tried many things and can't get it.

    The points P(-2,1),Q(-6,4),and R(4,3) are three vertices of parrallelogram PQRS
    a) Find the coordinates of S
    You don't need to use the dot product here, in fact, all we need to do is construct the diagram.

    This is what our diagram should look like: Parallelogram - Wikipedia, the free encyclopedia

    So graph the points you have and label the remaining point in the vacent corner S and draw lines to it.

    The height of the known side (point Q to point P) is  4-1 = 3 and the right side of the diagram has point R at height 3. We know that, by the shape of the parallelogram S needs to be bellow R, so its height or y co-ordinate is  3-3=0

    The same procedure but for the x-cordinate between R and Q yields  -6-4 = -10 . Thus, the x co-cordinate for S is  -2 - - 10 = 8

    S is at (8, 0)
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by canadasbest View Post
    Ok heres the question i am stuck on. I have tried many things and can't get it.

    The points P(-2,1),Q(-6,4),and R(4,3) are three vertices of parrallelogram PQRS
    a) Find the coordinates of S
    Treating as 2-vectors:

    PQ=Q-P

    QR=R-Q

    RS=S-R

    But this is a paralleogram so RS=-PQ hence:

    S=R-PQ=R-Q+P

    CB
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Inner product problem
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: October 15th 2010, 07:58 PM
  2. Product problem.
    Posted in the Algebra Forum
    Replies: 4
    Last Post: August 7th 2009, 08:58 AM
  3. Inner product problem
    Posted in the Advanced Algebra Forum
    Replies: 6
    Last Post: June 6th 2008, 07:41 AM
  4. Dot Product Problem
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 16th 2008, 10:08 AM
  5. Inner product problem
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: April 2nd 2008, 11:51 PM

Search Tags


/mathhelpforum @mathhelpforum