Results 1 to 2 of 2

Math Help - directional derivatives

  1. #1
    Newbie
    Joined
    Mar 2012
    From
    USA
    Posts
    1

    directional derivatives: NEED CLARIFICATION :(

    compute the directional derivatives of f in the given directions V at the given points p f(x,y,z)=xy^2 +y^2z^3 + z^3x, p=(4,-2,-1), v=(1/ sqroot14) (i + 3j + 2k)

    after you find the partial derivative of x,y, and z, i know you have to use the formula: (partial dervative of x)(v1) + (partial dervative of y)(v2) + (partial dervative of z)(v3) BUT do i just mulitple 1/sqroot14 to i, j and k OR do I assume v=(1/ sqroot14) (i + 3j + 2k) is in the (v)/(||v||) form and v1,v2,v3 is actually 1, 3, and 2 respectively?
    Last edited by xsammii; March 12th 2012 at 06:37 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Mar 2012
    From
    Planet Earth
    Posts
    1

    Re: directional derivatives

    Yes, you have to multiply the 1/sqrt(14) to the vector and then take the dot product of f and v. However, you should also multiply v by the reciprocal of the magnitude of v. In other words, find the normal of v.

    n=1/sqrt(4^2+(-2)^2+(-1)^2) = 1/sqrt(21)

    n*v =( sqrt(6)/42)(i + 3j + 2k)


    Check this link with tons of examples and solutions. Go directly to page 8 and you'll see an example of your question. Also, read about DOT PRODUCT.

    http://www.tech.plym.ac.uk/maths/res...X/gradient.pdf
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Directional derivatives
    Posted in the Calculus Forum
    Replies: 5
    Last Post: April 6th 2011, 09:28 PM
  2. directional derivatives!?
    Posted in the Calculus Forum
    Replies: 2
    Last Post: November 6th 2008, 11:45 AM
  3. directional derivatives
    Posted in the Calculus Forum
    Replies: 3
    Last Post: November 5th 2008, 07:08 PM
  4. Directional Derivatives
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 24th 2008, 01:55 PM
  5. Directional derivatives
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 5th 2008, 03:51 PM

Search Tags


/mathhelpforum @mathhelpforum