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!

Homework Help: Lines and planes

  1. Nov 18, 2008 #1
    1. The problem statement, all variables and given/known data

    show that the plane 2x - y + 4z = 81

    never intersects the line


    2. Relevant equations


    3. The attempt at a solution

    I wanted to show that the line and the plane were parallel. So the unit vector for the line would be 3i + 3j + 1k
    Then I get confused how to show this is parallel to the plane
    Planes don't have unit vectors do they ?
    The vector normal to the plane i suppose is 2i + -j + 4z

    So if the two were parallel a dot b would be = 0
    but this doesnt work ... help
  2. jcsd
  3. Nov 18, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    I think the unit vector of the line is 3i+2j+k. But that doesn't change anything, the direction vector and the normal vector still aren't perpendicular. That can only mean that the line and the plane must intersect. There is probably a typo in the problem.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook