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!

Integration by Subtitution: sin(x).cos(x).(e^cos(x))

  1. Jul 23, 2011 #1
    Problem attached as image. Solution included.

    I am fine with getting the integrating factor, that bits the easy bit obviously.
    But Basically my specific problem is when I try to integrate sin(x).cos(x).(e^cos(x))

    I understand that I need to use substitution here, but I'm not sure how they have done it.
    Why does the sin(x) suddenly disappear? Where did it go during the substitution?

    Can someone please explain this for me? many thanks in advance.
     

    Attached Files:

  2. jcsd
  3. Jul 23, 2011 #2

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If u = cos(x) then du = -sin(x)dx. It's in the du.
     
  4. Jul 23, 2011 #3
    I suspected that but I then I got upset because I didn't know where the -ve went?
     
  5. Jul 24, 2011 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    There seems to be a "typo" in the attached document.

    RGV
     
  6. Jul 27, 2011 #5
    arghh hate that. cheers guy, appreciated.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Integration by Subtitution: sin(x).cos(x).(e^cos(x))
  1. Cos x and Sin x (Replies: 11)

  2. Integral of cos(e^x) (Replies: 8)

  3. Integral of x*e^cos(x) (Replies: 3)

Loading...