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: Differentiate part 2

  1. Mar 8, 2008 #1
    1. The problem statement, all variables and given/known data

    RE: F(y)= (1/y[tex]\hat{}2[/tex] - 3/y[tex]\hat{}4[/tex])(y+5y)
    the answer is: F=5+14/y[tex]\hat{}2[/tex]+9/y[tex]\check{}4[/tex]

    3. The attempt at a solution

    F(y)= (f*g)[tex]\acute{}[/tex]

    so, I get (14/y[tex]\hat{}2[/tex] +9/y[tex]\hat{}4[/tex])+5y,
    which is very close to the answer in the book, except that instead of 5y they have the answer as just (14/y[tex]\hat{}2[/tex] +9/y[tex]\hat{}4[/tex])+5
  2. jcsd
  3. Mar 8, 2008 #2
    I cannot clearly read what you did, but you first need to apply the product rule tha is
    let [tex] f(y)=y^{-2}-3y^{-4}, \ \ and \ \ \ g(y)=6y[/tex] so


    or you could merely foil everyghing out and you would end up with:

    [tex]F(y)=6y^{-1}-18y^{-3}[/tex] and then take the derivative of this one.

    However i think that you originally gave us the wrong function, for there is no way you can get the answer you provided us. check it again, for i won't do it for you. Because by just integrating the result you gave us, one cannot get the function you provided.
    Last edited: Mar 8, 2008
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook