1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: U substitution

  1. May 27, 2009 #1
    [ ( x^2 ) ( sinx ) ] / (1 + x^6)
  2. jcsd
  3. May 27, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor

  4. May 27, 2009 #3


    Staff: Mentor

    Cristo, I get 42. You might have forgotten to multiply by Hooker's constant (= 2.413793103).
  5. May 27, 2009 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Don't listen to these clowns. The answer you seek is

    [ ( u^2 ) ( sinu ) ] / (1 + u^6)
  6. May 28, 2009 #5


    Staff: Mentor

    That's an extremely useful substitution in those cases where you find the given variable esthetically displeasing for some reason.

    For all other cases, not so much.
  7. May 28, 2009 #6


    Staff: Mentor

    If you're still out there, you would have gotten more serious (and helpful) responses if you had given us the complete problem. We can infer that this is an integration problem, although there was no indication of that in what you wrote. Also, if you want help, show us what you've tried.

    The integral looks to me like it could be done using integration by parts in this way:
    u = cos x
    [tex]dv = \frac{x^2 dx}{1 + x^6}[/tex]

    To find v, you'll have to integrate dv, which involves a substitution w = x3, dw = 3x2dx. I haven't worked it out, but this is what I would try first.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook