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: Equation of plane

  1. Jun 21, 2007 #1
    1. The problem statement, all variables and given/known data
    Find the equation of the plane that passes throughthe point (-1,2,1) and contains the line of intersection of the planes x+y-z=2, and 2x-y+3=1

    2. Relevant equations

    3. The attempt at a solution
    My reasoning is that we can take the normal vectors of the given planes, take the cross product, which will be orthoganol to the plane we want.
    We then just plug the obtained normal vector and the point into the equation. Right?
  2. jcsd
  3. Jun 21, 2007 #2
    that's correct
  4. Jun 21, 2007 #3
    Just wanted to check.
    I get an anwer but it is wrong from the books, so it must be my doing.
  5. Jun 21, 2007 #4
    put up your calculations in tex and i'll follow em through
  6. Jun 21, 2007 #5
    Shouldn't you find the the line of intersection? And then the direction from the point (-1,2,1) to a point on the line? And then find a vector perpendicular to the two directions? And then pick any point that you know is going to be on your plane to satisfy your scalar equations?
  7. Jun 22, 2007 #6
    yea thats right, i wasn't thinking straight. how do you find a vector that's perpindicular to the vector that points from the (-1,2,1) to the line of intersection? find a vector which when crossed with it = 0?
  8. Jun 22, 2007 #7

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    What is the angle between the cross product of two vectors and either of the two multiplicand vectors?
  9. Jun 22, 2007 #8
    90deg , yea just cross the vector from (-1,2,1) and the line of intersection to the normal vector of the plane
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook