1. Not finding help here? Sign up for a free 30min 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!

Very simple derivative

  1. Nov 6, 2008 #1
    1. The problem statement, all variables and given/known data
    3/x^2

    when I take the quotient rule ,
    I get:
    (0*x^2-3*2x)/(x^2)^2
    isn't that -6x/x^4 or -6/x^3
    My calculator says -6 and so it is, but why and what am I missing?
     
  2. jcsd
  3. Nov 6, 2008 #2
    ok From what i see you are right.the answer is -6x^-3.

    but at what point are you evalusting.did they give you a point or did you just type on your calculator.you have to have value of x.to type on your calculator
     
  4. Nov 6, 2008 #3
    I originally had to differentiate f(t)=cos^-1(3/t^2)
    my answer was f'(t)=-1/sqrt(1-(3/t^2)^2)*-6t
    f'(t)=6t/sqrt(1-9/t^4)
    I got the "-6t" part wrong, it was supposed to be just -6.

    when I differentiate just 3/x^2 into my calculator and it comes out -6
    on my ti89 calc. I go to math, calculus, differentiate and type in:
    d(3/x^2,x) and get -6
     
  5. Nov 6, 2008 #4
    Instead of using the quotient rule, you might find it easier to evaluate
    3 x^-2
     
  6. Nov 6, 2008 #5
    Oky, thanks. I see my problem.
    I should have looked into the mirror sooner, the problem was there all along!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?