Results 1 to 5 of 5

Math Help - trig derivative

  1. #1
    Member
    Joined
    Sep 2011
    Posts
    106
    Thanks
    1

    trig derivative

    what it the derivative of (cosX)^3 using rules

    Is it as easy as 3(-sinX)2 =-3sin^2X ?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    12,128
    Thanks
    1009

    Re: trig derivative

    Quote Originally Posted by delgeezee View Post
    what it the derivative of (cosX)^3 using rules

    Is it as easy as 3(-sinX)2 =-3sin^2X ?
    \frac{d}{dx} (\cos{x})^3 = 3(\cos{x})^2 \cdot (-\sin{x})
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    29

    Re: trig derivative

    You need to use the chain rule here

    Find  (\cos^3x)'

    Let's make  y=\cos^3x and  u=\cos x\implies y=u^3

    So  \frac{dy}{du} = 3u^2 and  \frac{du}{dx} = -\sin x

    By the chain rule \frac{dy}{dx}= \frac{dy}{du}\times  \frac{du}{dx}

    Can you finish it?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Oct 2011
    Posts
    13

    Re: trig derivative

    Chain rule. 3(cosx)^2(-sinx)
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Sep 2011
    Posts
    106
    Thanks
    1

    Re: trig derivative

    Thanks, I understand now.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Trig Derivative
    Posted in the Calculus Forum
    Replies: 2
    Last Post: June 10th 2010, 12:25 AM
  2. trig derivative help...
    Posted in the Calculus Forum
    Replies: 2
    Last Post: February 21st 2010, 01:02 PM
  3. Trig Derivative
    Posted in the Calculus Forum
    Replies: 3
    Last Post: October 18th 2009, 04:24 AM
  4. help with a trig derivative?
    Posted in the Calculus Forum
    Replies: 11
    Last Post: October 4th 2008, 08:22 PM
  5. Please help me with a trig derivative
    Posted in the Calculus Forum
    Replies: 1
    Last Post: January 30th 2007, 02:38 PM

/mathhelpforum @mathhelpforum