1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Parametric equations and symmetric equations

  1. Aug 30, 2011 #1
    1. The problem statement, all variables and given/known data

    Find parametric equations and symmetric equations for the line through the points (0,1/2,1) and (2,1,-3)



    2. Relevant equations



    3. The attempt at a solution

    I started out graphing the points and connecting them with a straight line. I called the first point P and second Q. So the vector PQ = <2,1/2,-4>. So my vector r_0 is <0,1/2,1> so vector r = r_0 + tv

    so <x,y,z>=<0,1/2,1> +t<2,1/2,-4>

    <x,y,z> = <0+2t, 1/2 + t/2, 1-4t>

    So my parametric equations are:

    x=2t
    y=1/2 + t/2
    z=1-4t

    And my symmetric eqs. are:

    x/2 = 2y-1 = (z-1)/-4

    This answer is wrong and I've done it a few times any hints? Thanks
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Aug 30, 2011 #2

    Mark44

    Staff: Mentor

    Looks good. This is what I get, too.
    Instead of 2y - 1, write the expression in the middle as (y - 1/2)/(1/2). This is equal to what you have, but if your work is being computer-graded, it might not be smart enough to recognize different forms of the same thing.
     
  4. Aug 30, 2011 #3
    It is not online homework. My paper actually says what you said to put but I found it easier to type so I multiplied by 2. So what do you think is wrong? Or is it right and there are multiple answers? Thanks.
     
  5. Aug 31, 2011 #4

    Mark44

    Staff: Mentor

    What you have is also correct, because 2y - 1 = (y - 1/2)/(1/2). If you multiply the expression on the right by 2/2, you get the expression on the left.
     
  6. Aug 31, 2011 #5
    Form a vector between the points:

    say : B-A= <2, 0.5, -4 >

    <x,y,z> - <2,1,-3> = k < 2, 0.5,-4>

    and so on...
     
  7. Aug 31, 2011 #6

    Mark44

    Staff: Mentor

    stallionx, if you had read the thread before posting, you would have discovered that the OP had already arrived at the solution.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook