Results 1 to 10 of 10

Math Help - Need help with couple of integrals!

  1. #1
    Junior Member
    Joined
    Jun 2010
    From
    Skopje
    Posts
    54

    Need help with couple of integrals!

    i got some probs. to solve this integrals :

    integral x*arctan(x)dx
    integral (11x+7)/(2x^2+7x-4)dx
    integral ln(x^2+1)dx
    intgral e^x/(1-e^3x)dx

    i tryed solving this but i get stucked somewhere the first one is with partial integration ,second one i substitute the denominator with u and i get 4x+7 for du and there i get stucked ,the third one is partial as well but again as the first one i get to a point where i need to solve integral x^2/(x^2+1) and this one is not rly simple i dont know to solve it so i need help there, the 4 one is also with sub. for u=e^x but then i get integral 1/1-u^3 i tryed to make sub. for t=1-u^3 so i can get one parameter in the denominator and two up and than devide in two integrals but i couldnt get it.. please some help if you know how to solve this , btw these are from faculty from exam sessions thanks!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Mar 2009
    Posts
    5
    Hi, right now I'm in a hurry. But I'd like to give you a very useful tip. You can always use the Wolfram Online Integrator to solve integrals.

    Wolfram Mathematica Online Integrator

    And then go back from there. I mean, try to understand which method to use from the anti-derivative. Good luck!
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Jun 2010
    From
    Skopje
    Posts
    54
    dude i tryed in mathematica it self i got it but i cant get till the result walking so it doesnt rly helped me even the online thingy is giving me the same result but it didnt help me i need some step by step solvation if anyone could do it thanks!
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor harish21's Avatar
    Joined
    Feb 2010
    From
    Dirty South
    Posts
    1,036
    Thanks
    10
    Quote Originally Posted by goroner View Post
    i got some probs. to solve this integrals :

    integral x*arctan(x)dx
    integral (11x+7)/(2x^2+7x-4)dx
    integral ln(x^2+1)dx
    intgral e^x/(1-e^3x)dx

    i tryed solving this but i get stucked somewhere the first one is with partial integration ,second one i substitute the denominator with u and i get 4x+7 for du and there i get stucked ,the third one is partial as well but again as the first one i get to a point where i need to solve integral x^2/(x^2+1) and this one is not rly simple i dont know to solve it so i need help there, the 4 one is also with sub. for u=e^x but then i get integral 1/1-u^3 i tryed to make sub. for t=1-u^3 so i can get one parameter in the denominator and two up and than devide in two integrals but i couldnt get it.. please some help if you know how to solve this , btw these are from faculty from exam sessions thanks!
    1) use integration by parts:
    \int u \mbox{dv} = uv -\int v \mbox{du}

    where  u = arctan(x),     dv = x dx
    du = \frac{1}{x^{2}+1} dx,     v = x^2/2:
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor harish21's Avatar
    Joined
    Feb 2010
    From
    Dirty South
    Posts
    1,036
    Thanks
    10
    Very few people might have the time to show step by step solutions to all 4 problems:

    check here. Click on show steps.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Junior Member
    Joined
    Jun 2010
    From
    Skopje
    Posts
    54
    for the 1 one i did use partial integration and i get to a point to solve integral of x^2/(x^2+1) and here i get stucked i need help to solve that one
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    Jun 2010
    From
    Skopje
    Posts
    54
    says x^2/(x^2+1) should be done with long division but dont know to do that .. ehm =/
    Follow Math Help Forum on Facebook and Google+

  8. #8
    MHF Contributor harish21's Avatar
    Joined
    Feb 2010
    From
    Dirty South
    Posts
    1,036
    Thanks
    10
    integrate x*arctan(x)dx - Wolfram|Alpha
    Quote Originally Posted by goroner View Post
    for the 1 one i did use partial integration and i get to a point to solve integral of x^2/(x^2+1) and here i get stucked i need help to solve that one
    Follow Math Help Forum on Facebook and Google+

  9. #9
    MHF Contributor harish21's Avatar
    Joined
    Feb 2010
    From
    Dirty South
    Posts
    1,036
    Thanks
    10
    Quote Originally Posted by goroner View Post
    says x^2/(x^2+1) should be done with long division but dont know to do that .. ehm =/

    You need to review your books/ notes:

    \frac{x^2}{x^{2}+1} = 1 - \frac{1}{x^2+1}

    Heard of partial fractions?

    \frac{x^2}{x^2+1} = A + \frac{B}{x^2+1}

    x^2 = A(x^{2}+1) + B

    solving for A and B gives the required result.
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Junior Member
    Joined
    Jun 2010
    From
    Skopje
    Posts
    54
    i did heard of partial fractions but i never solve one like this , mostly i was solving partial fractions with factors in the denominator ,anyways thanks for this a lot!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 14
    Last Post: April 6th 2011, 10:22 AM
  2. a couple more definite integrals
    Posted in the Math Challenge Problems Forum
    Replies: 2
    Last Post: March 31st 2011, 08:44 AM
  3. a couple of trigonometric integrals
    Posted in the Calculus Forum
    Replies: 7
    Last Post: December 27th 2010, 07:43 AM
  4. a couple integrals
    Posted in the Calculus Forum
    Replies: 4
    Last Post: April 18th 2008, 12:20 PM
  5. A couple of indefinite integrals
    Posted in the Calculus Forum
    Replies: 5
    Last Post: September 18th 2006, 12:29 AM

Search Tags


/mathhelpforum @mathhelpforum