Results 1 to 4 of 4

Math Help - integration by parts

  1. #1
    Junior Member
    Joined
    Jul 2007
    Posts
    72

    integration by parts

    I am stuck on how to do these types of problems by using integration by parts.

    intergral sign xsec^2(3x)dx
    I set fprime to sec^2(3x)
    I set g = x, gprime = 1.
    I dont know what f equals in this scenario and dont know how to solve it. Thanks.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by davecs77 View Post
    I am stuck on how to do these types of problems by using integration by parts.

    intergral sign xsec^2(3x)dx
    I set fprime to sec^2(3x)
    I set g = x, gprime = 1.
    I dont know what f equals in this scenario and dont know how to solve it. Thanks.
    As \frac{d}{dx}\tan(x)=\sec^2(x), we have:

    \frac{1}{3}\frac{d}{dx}\tan(3x)=\sec^2(3x).

    RonL
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Jul 2007
    Posts
    72
    Quote Originally Posted by CaptainBlack View Post
    As \frac{d}{dx}\tan(x)=\sec^2(x), we have:

    \frac{1}{3}\frac{d}{dx}\tan(3x)=\sec^2(3x).

    RonL
    How would you solve the problem then?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Eater of Worlds
    galactus's Avatar
    Joined
    Jul 2006
    From
    Chaneysville, PA
    Posts
    3,001
    Thanks
    1
    Let u=x, \;\ dv=sec^{2}(3x)dx, \;\ du=dx, \;\ v=\frac{tan(3x)}{3}

    uv-\int{v}du

    \frac{xtan(3x)}{3}-\frac{1}{3}\int{tan(3x)}dx

    Now, continue?.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: January 11th 2012, 03:30 PM
  2. Replies: 8
    Last Post: September 2nd 2010, 01:27 PM
  3. Replies: 0
    Last Post: April 23rd 2010, 04:01 PM
  4. Integration by Parts!
    Posted in the Calculus Forum
    Replies: 7
    Last Post: January 22nd 2010, 04:19 AM
  5. Replies: 1
    Last Post: February 17th 2009, 07:55 AM

Search Tags


/mathhelpforum @mathhelpforum