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!

Derivatives: help?

  1. Aug 19, 2008 #1
    1. The problem statement, all variables and given/known data
    Prove using the definition of a derivative.
    If y=sinx, then y1=cosx


    2. Relevant equations
    .. ? identities maybe..? i dont really know much about derivatives..


    3. The attempt at a solution
    y = sinx..
    y1 = (1)sinx^1-1
    y1 = 1..
    how is that suppose to equal cosx?? !
    i havent got a clue, any help would really be appreciated!!
    :shy:
     
  2. jcsd
  3. Aug 19, 2008 #2

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    What is the definition of the derivative?
     
  4. Aug 19, 2008 #3
    ?? i'm not all that certain..
    its got somethink to do with graphs, but..
    idk, i been looking at a graph of y = sinx
    but i dont know what to do with it: oy
     
  5. Aug 19, 2008 #4

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

  6. Aug 19, 2008 #5
    .. ?
    woahw.. so... how do i apply that
    to the sin graph?..
    : no clue..
    maybe i'll go over it again..
     
  7. Aug 19, 2008 #6

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    You set f(x)=sin(x) in the expression [tex] f'(x)=\lim_{h\to0}\;\frac{f(x+h)-f(x)}{h}[/tex]


    Hint: if you actually read through that thread, then you may be surprised as to what you find...

    I'm moving this to calc&beyond, since it is calculus!
     
  8. Aug 19, 2008 #7
    .. i dont think i understand the formula..
    : f(x) = sinx .. then.
    = sinx = lim(h-->) sin(x+h) - sinx/ h
    ... this is so wrong
    wait, what is h?..
     
  9. Aug 19, 2008 #8

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    Have you studied limits before? From your posts here, it sounds like you haven't. This problem will be incredibly difficult if you have not heard about limits before, and I can't see why it would have been set for you to try.
     
  10. Aug 19, 2008 #9
    ^^ i dont know why either!!
    ahhahaa!! i think i'll just skip it for now..
    thanks for your help
     
  11. Aug 19, 2008 #10
    Try learning limits, then the definition of derivative, then the squeeze theorem and then you should be able to make a fairly decent proof of it.
     
  12. Aug 19, 2008 #11
    Skipping is not possible if you are learning about derivatives right now.
    This will haunt you later :blushing:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Derivatives: help?
  1. Help with a Derivative (Replies: 2)

  2. Help with derivative (Replies: 19)

  3. Help with derivative (Replies: 1)

Loading...