Results 1 to 3 of 3

Math Help - diff eqn, sin(2x).

  1. #1
    Junior Member
    Joined
    Feb 2009
    Posts
    34

    diff eqn, sin(2x).

    d3y/dx3+dy/dx=sin(2x). Here, i get as far as to lambda is 0,i,-i. Thereafter, I am not sure even how to write this in general form, let alone what to do with that sin thingy... can someone please help?
    Also given is: y(0)=1, dy/dx(0)=0, d2y/dx2=0.
    Last edited by fiksi; March 11th 2009 at 12:52 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member
    Joined
    Feb 2009
    Posts
    34
    Quote Originally Posted by fiksi View Post
    d3y/dx3+dy/dx=sin(2x). Here, i get as far as to lambda is 0,i,-i. Thereafter, I am not sure even how to write this in general form, let alone what to do with that sin thingy... can someone please help?
    Also given is: y(0)=1, dy/dx(0)=0, d2y/dx2=0.
    it's not = and =, it was +... corrected it now.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Mar 2008
    Posts
    61
    Quote Originally Posted by fiksi View Post
    d3y/dx3+dy/dx=sin(2x). Here, i get as far as to lambda is 0,i,-i. Thereafter, I am not sure even how to write this in general form, let alone what to do with that sin thingy... can someone please help?
    Also given is: y(0)=1, dy/dx(0)=0, d2y/dx2=0.
    Hello fiksi,

    I assume that you can find the solution for the homogeneous equation, it is:

    y_h=A+B\cdot cos(x)+C\cdot sin(x)

    Now, what you need to use as particular solution is:

    y_p=D\cdot sin(2x)+ E\cdot cos(2x)

    Substitute this in the original DE and it will give you a system for finding D and E. (they are 0 and 1/6)

    best regards,

    Coomast
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Diff Eq. x' = t * cos(t)
    Posted in the Differential Equations Forum
    Replies: 3
    Last Post: April 2nd 2010, 06:16 PM
  2. Diff eq IVP
    Posted in the Differential Equations Forum
    Replies: 2
    Last Post: December 10th 2009, 02:05 PM
  3. diff eq help
    Posted in the Differential Equations Forum
    Replies: 1
    Last Post: January 25th 2009, 02:16 PM
  4. Diff Qn'
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 29th 2008, 09:35 AM
  5. diff eq help
    Posted in the Calculus Forum
    Replies: 0
    Last Post: March 31st 2008, 04:41 PM

Search Tags


/mathhelpforum @mathhelpforum