1. Limited time only! Sign up for a free 30min personal 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!

Chain rule differentiation

  1. Jun 16, 2014 #1
    The question:
    ImageUploadedByPhysics Forums1402924990.055025.jpg
    This is the solution that was given by my teacher


    I understand how the work is done until the 3-4 line. Where did the 1-cos2x disappear to in the 4th line?
    I know you can use the outside inside method but try as I might, I can't seem to understand how the final answer was gotten??

    Can someone please tell me what I'm missing here??
  2. jcsd
  3. Jun 16, 2014 #2

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    What is ##(1+\cos(2x)) + (1-\cos(2x))## ?
  4. Jun 16, 2014 #3
    The differentiation is done from line 1 to line 2. The rest is just tidying things up a little. The equality from line 3 to line 4 follows simply because

    2\sin(2x)(1 + \cos(2x)) + 2\sin(2x)(1 - \cos(2x)) =2 \sin(2x)( 1 + \cos(2x) + 1 - \cos(2x)) = 4 \sin(2x).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted