1. Not finding help here? Sign up for a free 30min 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!

Working problem 3 ways

  1. Jun 26, 2005 #1
    I have to work this problem 3 ways, and I've gotten two, but am not sure about the third way.

    integral (x/sqrt(x^2-9))dx
    the first way I worked by setting u = x^2 - 9
    the second way I worked by setting x = 3sec(theta)
    but the third way I have no clue, the book gave us a hint: Let x^2 - 9 = (sin(theta))^2

    Thanks
     
  2. jcsd
  3. Jun 26, 2005 #2
    Do exactly what you did with x = 3sec(theta), but this time with the identity x^2 - 9 = (sin(theta))^2.

    x = sqrt((sin(theta)^2)+9);
    dx = sin(theta)cos(theta)(((sin(theta)^2)+9)^-.5) d(theta)

    Plug that in (and the x^2 value) and solve; you answer should come up to be sin(theta) + C. Then all you need to do is change back in terms of x.
     
    Last edited: Jun 26, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?