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: Two vectors to be parallel

  1. Aug 5, 2010 #1
    1. The problem statement, all variables and given/known data
    What is the condition of two vectors to be parallel?
    if A= A1i+A2j+A3k and B=B1i+B2j+B3k then what is the condition that the two vectors are parallel..

    2. Relevant equations

    A*B=AB sin(theeta)

    3. The attempt at a solution

    by cross product i find the condition
    A1/B1=A2/B2=A3/B3 .... under which determinant becomes equal to to 0. which is the condition for parallel..theeta = 0 so sin 0 = 0 ... kindly confirm is it write or wrong.
     
  2. jcsd
  3. Aug 5, 2010 #2
    Two vectors are parallel if their cross product is the zero vector.
     
  4. Aug 5, 2010 #3

    Mark44

    Staff: Mentor

    Also, two vectors are parallel if either is a constant multiple of the other.
     
  5. Aug 6, 2010 #4

    HallsofIvy

    User Avatar
    Science Advisor

    Specifically, [itex]A_1\vec{i}+ A_2\vec{j}+ A_3\vec{k}[/itex] and [itex]\B_1\vec{i}+ B_2\vec{j}+ B_3\vec{k}[/itex] are parallel if and only if
    [tex]\frac{A_1}{B_1}= \frac{A_2}{B_2}= \frac{A_3}{B_3}[/tex]
     
  6. Aug 6, 2010 #5
    thank you hall
     
  7. Aug 8, 2010 #6

    HallsofIvy

    User Avatar
    Science Advisor

    Well, I just said what Mark44 said!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook