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: Evaluate integral

  1. Feb 6, 2009 #1
    1. The problem statement, all variables and given/known data

    between pi/2 and pi/6[tex]\int[/tex] (cos x) / (7 + sin x)

    move 1/7 to the out side

    1/7 [tex]\int[/tex] cos x / sin x

    u= sin x
    du= cos x

    so i get
    1/7 ln sinx + C

    then plug pi/2 minus pi/6???
  2. jcsd
  3. Feb 6, 2009 #2


    Staff: Mentor

    You can't do that.

    Is [tex]\frac{1}{7 + 3} = 1/7 * \frac{1}{3}[/tex]

    Instead, you might try multiplying by (7 - sin(x))/(7 - sin(x)).
  4. Feb 6, 2009 #3


    User Avatar
    Science Advisor

    If you are taking calculus, your algebra should be better than that! cos(x)/(7+ sin(x)) is NOT (1/7) cos(x)/sin(x).

    Instead use the substitution u= 7+ sin x.

    Mark got in just ahead of me but I think my suggestion for integrating it is easier!
    Last edited by a moderator: Feb 6, 2009
  5. Feb 6, 2009 #4
    k got it
    i have taken any math for 2 year and i am now taking cal 2 so yea... but i solved it thanks
  6. Feb 6, 2009 #5


    Staff: Mentor

    Yes, I agree. It just goes to show that "haste makes waste."
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook