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: Proving Vector Properties

  1. Jun 13, 2008 #1
    I can't seem to figure out how to prove the property for R(t) = <f(t), g(t), h(t)> :

    Dt[R(t) X R'(t)] = R(t) X R"(t)

    Any suggestions?!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 13, 2008 #2


    User Avatar
    Homework Helper

    is X cross product?
    [R(t) X R'(t)]' = R'(t) X R'(t)+R(t) X R"(t)
    for any sensible derivative
    [R(t) X R'(t)]' = R(t) X R"(t)
    if and only if
    R'(t) X R'(t)=0
    clearly true for cross product
  4. Jun 13, 2008 #3


    User Avatar
    Science Advisor

    Is the "Dt" derivative with respect to t? i.e.(R x R')' ?

    What have you tried? Have you tried actually writing out each side in terms of derivatives of f, g, and h?

    Do you know that the "product rule" from Calculus I is still true for vector products? What does that give you?
  5. Jun 13, 2008 #4
    wow.. I had copied the property [R(t) x R'(t)]' = blah blah blah.. incorrectly from my book... It makes perfect sense now, thank you for the help!!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook