Results 1 to 5 of 5

Math Help - Trigonometry Integration

  1. #1
    Super Member
    Joined
    Sep 2007
    Posts
    528
    Awards
    1

    Trigonometry Integration

    How do I do this:

    \displaystyle\int (\sin 2x.\sin x) dx

    ---------------------------------------------

    The Answer is:
    \frac {2}{3} \sin^3x + c


    Thank you advance.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,605
    Thanks
    1574
    Awards
    1
    \sin (2x)\sin (x)dx = 2\sin ^2 (x)\left[ {\cos (x)dx} \right]
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    Sep 2007
    Posts
    528
    Awards
    1
    Quote Originally Posted by Plato View Post
    \sin (2x)\sin (x)dx = 2\sin ^2 (x)\left[ {\cos (x)dx} \right]

    How is cosx cancelled out? When I use the cosx double angle rule to integrate sinx, I don't obtain the correct answer. Can you show the stages please?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,605
    Thanks
    1574
    Awards
    1
    No I will not do the problem for you.
    But what you have is 2 u^2 du.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    GAMMA Mathematics
    colby2152's Avatar
    Joined
    Nov 2007
    From
    Alexandria, VA
    Posts
    1,172
    Awards
    1
    Quote Originally Posted by Air View Post
    How is cosx cancelled out? When I use the cosx double angle rule to integrate sinx, I don't obtain the correct answer. Can you show the stages please?
    sin(2x)=2sin(x)cos(x)
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Integration with trigonometry
    Posted in the Calculus Forum
    Replies: 6
    Last Post: May 1st 2010, 07:32 AM
  2. Integration with trigonometry
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: May 1st 2010, 06:04 AM
  3. Integration problem with trigonometry
    Posted in the Calculus Forum
    Replies: 1
    Last Post: March 3rd 2010, 08:34 PM
  4. integration of inverse trigonometry
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 4th 2009, 02:58 AM
  5. Replies: 1
    Last Post: September 25th 2009, 07:24 AM

Search Tags


/mathhelpforum @mathhelpforum