Results 1 to 6 of 6

Math Help - Confusing Integral

  1. #1
    Newbie
    Joined
    Jun 2009
    Posts
    1

    Confusing Integral

    Does anybody know how to go about solving this integral:

    cos(2x+1)cos(4x-2)sin(x) dx

    I've tried a number of methods but can't seem to finish it...
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Math Engineering Student
    Krizalid's Avatar
    Joined
    Mar 2007
    From
    Santiago, Chile
    Posts
    3,654
    Thanks
    13
    You can turn the product \cos\alpha\cos\beta into a sum of cosines, then expand and you'll get terms like \cos\alpha\sin\gamma and then you can turn that product into a sum.

    See here: List of trigonometric identities - Wikipedia, the free encyclopedia
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jun 2009
    Posts
    7

    Still having problems with this

    I tried that method, or at least, tried to do that method: I ended up with ∫cos(2x+1)cos(2-4x)sinxdx

    1) I expanded the cos's that are multiplied by each other with the cosAcosB property.
    2) I then used the cosA +cosB property, which simplified to what I wrote above, which isn't really an improvement.

    What am I doing wrong?
    (Steps would be appreciated)
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Jun 2009
    Posts
    7

    Answer!

    Not sure how to solve this integral problem? - Yahoo! Answers

    Look at the bottom submission, very helpful!
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by kelseyk23 View Post
    Not sure how to solve this integral problem? - Yahoo! Answers

    Look at the bottom submission, very helpful!
    Yes. Very helpful. No doubt you will duly reference this solution in the work you submit (since most colleges, http://berkeley.edu/ for example, otherwise take a dim view of this sort of thing ....)
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Jun 2009
    Posts
    7
    @ Mr. Fantastic,

    We have to reference that? I realize you think it would be plagiarism to take that work and submit it as homework, but that would only be true if one were to completely take someone else's work. I'd already solved most of the problem before I got an answer on there. Just because someone else actually submitted a full length response doesn't mean that I, or anyone else, hadn't solved it before hand. If someone gives you a helpful hint, I view that as tutoring. My school expects you to go get tutoring, but it's not expected that you cite your tutor for their guidance.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Confusing Integral!
    Posted in the Calculus Forum
    Replies: 8
    Last Post: February 6th 2011, 10:10 AM
  2. Confusing integral question
    Posted in the Calculus Forum
    Replies: 1
    Last Post: October 29th 2010, 06:17 AM
  3. Confusing integral
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 20th 2010, 09:34 AM
  4. confusing integral
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 15th 2010, 02:44 AM
  5. Confusing integral
    Posted in the Calculus Forum
    Replies: 4
    Last Post: March 2nd 2009, 08:20 PM

Search Tags


/mathhelpforum @mathhelpforum