Results 1 to 7 of 7

Math Help - Integration

  1. #1
    Junior Member
    Joined
    Apr 2009
    Posts
    33

    Integration

    integrate xSquareroot(x^2+2x+4) dx
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,393
    Thanks
    1327
    Quote Originally Posted by mikegar813 View Post
    integrate xSquareroot(x^2+2x+4) dx
    Complete the square: x^2+ 2x+ 4= x^2+ 2x+ 1+ 3= (x+1)^2+ 3. First let u= x+1, then use a trig substitution.

    This is the third question you have asked with any indication of what you have tried yourself. If you do not show your own work, I will not respond to any more questions.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Apr 2009
    Posts
    33
    i just needed help starting them i will work them and post my work and answers. thanks.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Junior Member
    Joined
    Apr 2009
    Posts
    33
    if u=x+1
    du=1 dx and when i substitute back in i get
    integrate x Squareroot(u^2+3) dx
    what do i do with the du since it doesn't match the x outside the squareroot?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Banned
    Joined
    Oct 2009
    Posts
    4,261
    Thanks
    2
    Quote Originally Posted by mikegar813 View Post
    if u=x+1
    du=1 dx and when i substitute back in i get
    integrate x Squareroot(u^2+3) dx
    what do i do with the du since it doesn't match the x outside the squareroot?

    If you substitute u = x + 1 then x = u - 1. You cannot leave that x out there of the square root after you do this!

    Tonio
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Junior Member
    Joined
    Apr 2009
    Posts
    33
    Quote Originally Posted by tonio View Post
    If you substitute u = x + 1 then x = u - 1. You cannot leave that x out there of the square root after you do this!

    Tonio

    The 'x' was already out side of the square root.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Banned
    Joined
    Oct 2009
    Posts
    4,261
    Thanks
    2
    Quote Originally Posted by mikegar813 View Post
    The 'x' was already out side of the square root.

    So what? When you make substitution in integrals you change ALL the x's for the substitution! You decided u = x + 1 <==> x = u-1 ? Then ALL the
    x's in the integral are changed into u-1...!

    Tonio
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 3
    Last Post: November 3rd 2010, 12:54 AM
  2. Replies: 2
    Last Post: November 2nd 2010, 04:57 AM
  3. Replies: 8
    Last Post: September 2nd 2010, 12:27 PM
  4. Replies: 2
    Last Post: February 19th 2010, 10:55 AM
  5. Replies: 6
    Last Post: May 25th 2009, 06:58 AM

Search Tags


/mathhelpforum @mathhelpforum