1. Limited time only! Sign up for a free 30min personal 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!

Linear alg. Who is really smart here and can solve this?

  1. Mar 8, 2009 #1
    1. The problem statement, all variables and given/known data

    1) x=3+t
    y=2-4t
    z=-5+11t

    2)12x+10y-4z=46

    Find the point where these two lines intersect.

    12x+10*0-4*0=46
    x=3,8...

    doesn´t make any sense



    2. Relevant equations





    3. The attempt at a solution
     
  2. jcsd
  3. Mar 8, 2009 #2

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    For starters, you don't have two intersecting lines....2) is the equation of a plane, not a line.

    Secondly, you are right: what you did doesn't make any sense.....why have you assumed that y=z=0 at the point of intersection?

    Just plug your parametric equations for x,y, and z into the equation of the plane and solve for t....what does that value of t make x,y and z?
     
  4. Mar 8, 2009 #3

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    cleopatra has already been told to do this twice on the other thread dedicated to this problem.
     
  5. Mar 8, 2009 #4

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    hmmm....yes, I see...

    Cleopatra, we are not here to do your homework for you, you need to show some attempt at a solution.

    And creating multiple threads for the same topic is against forum rules.
     
  6. Mar 8, 2009 #5
    36+12t+20-40t+20-44t=46
    t=30/76


    ???
     
  7. Mar 8, 2009 #6

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    First of all let's be clear on the question.
    Does it really say "find the point where these two lines intersect"?
    Because I definitely get a line of intersection.
     
  8. Mar 8, 2009 #7
    yes it says "point". That´s why it confuses me as well.
     
  9. Mar 8, 2009 #8

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    There you go. Well done. Now you can use your value of t to find x, y and z.
    Ooops. Wait a minute. t isn't 30/76. Check your arithmetic.
     
  10. Mar 8, 2009 #9

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    Careful; 44+40-12=72 not 76 :wink:
     
  11. Mar 8, 2009 #10

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    You might want to recheck your calculation then:wink:
     
  12. Mar 8, 2009 #11

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    How do you figure? Do you mean the line lies in the plane? I don't think so.
     
  13. Mar 8, 2009 #12

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    Why does this confuse you?

    Imagine a sheet of paper as the plane, and your pencil as the line....if you lie your pencil flat on the paper, then the intersection is the entire line, but if you just poke a whole through the piece of paper and slide your pencil part way through it, the intersection is just a point.....you can also make it so the two don't intersect at all by holding the pencil a few inches above the paper.

    In this case, the line and the plane intersect at a point.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Linear alg. Who is really smart here and can solve this?
  1. Linear Alg. Proof (Replies: 2)

Loading...