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: Scalar product of vectors

  1. Apr 4, 2010 #1
    [PLAIN]http://img62.imageshack.us/img62/5319/49966749.png [Broken]

    What is the scalar multiples of a vector actually?
    I was thinking L = c[2 1 2]T
    Then I looked for projection of v on L. But I got c in my answers which are not supposed to be...
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 4, 2010 #2


    Staff: Mentor

    Every vector in L is some scalar multiple of <2, 1, 2>. The line goes through the origin - the zero multiple of this vector is 0<2, 1, 2> = <0, 0, 0>, a vector that starts and ends at the origin. The line goes through the point (-4, -2, -4), which you can get by taking the -2 multiple of the vector.

    For the reflection of v in the line, you want to find another vector w that is in the same plane as v and L, but is on the opposite side of L, and makes the same angle with L.
    Last edited by a moderator: May 4, 2017
  4. Apr 4, 2010 #3
    So I have to find angle theta between v and L, and then find vector w with negative theta?
    I also have to find the plane of v and L by cross product of v and L ....
    Last edited: Apr 4, 2010
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook