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: Can't figure out this seperable diffEQ!

  1. Feb 8, 2006 #1
    Can't figure out this seperable diffEQ! :(

    Hello everyone 'ive been trying to figure out this easy looking Differential Equation and yet its wrong! weee!
    Here is the problem:
    http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/58/6217226076d5fd259f53ad1e3ed4071.png [Broken]
    has an implicit general solution of the form F(x,y) = K.
    In fact, because the differential equation is separable, we can define the solution curve implicitly by a function in the form
    F(x,y) = G(x) + H(y) =K.

    Find such a solution and then give the related functions requested.
    F(x,y) = G(x) + H(y) = ?

    I submitted:
    http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/5a/1bcf742ffddc932f739864bc6d3e4a1.png [Broken]
    which was wrong.

    here is my work:
    http://img202.imageshack.us/img202/9317/lastscan6uc.jpg [Broken]

    Any help would be fantastical. <--yeah i'm pretty sure thats not a word.:bugeye:
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Feb 8, 2006 #2


    User Avatar
    Homework Helper

    Go back and insert a pair of parens on the left hand side of the second line that it would read

    [tex]\int e^y(\sin y+9\cos y) dy = \int(14x+5)dx[/tex]
  4. Feb 8, 2006 #3


    User Avatar
    Homework Helper

    Know also that

    [tex]\int e^y(\sin y+9\cos y) dy = e^y(5\sin y+4\cos y)[/tex]

    and in closing note that fantastical is now a word by extension, since, for example antideparameterizationism is likwise wise a word, for I am very much opposed to not eliminating a perfectly useful paramter from my solutions (especially once they've been obtained by inserting it cleverly into the givens,) and I am thus a practioner of antideparameterizationalism. :rofl:
    Last edited: Feb 8, 2006
  5. Feb 8, 2006 #4
    hah i like your way of thinking.
    I submitted
    http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/08/74e463c2a0d2a1740eacdf142dadd41.png [Broken]
    and they told me to f off, i was quite distraught. Any ideas what i did now
    Last edited by a moderator: May 2, 2017
  6. Feb 8, 2006 #5


    User Avatar
    Homework Helper

    try writing it in the order (fcn. of x) + (fcn. of y), e.g. G(x) + H(y), such as

    -7*x^2-5*x + 5*exp(y)*sin(y)+4*exp(y)*cos(y)
  7. Feb 8, 2006 #6
    ur the man!
    For some reason, i had to multiply through -1 to make it work, it loved this answer:http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/e6/513e4938c92e397902bfbf80c0e9551.png [Broken]
    Last edited by a moderator: May 2, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook