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: Implicit and explicit solution for a given initial-value problem

  1. Sep 25, 2011 #1
    The equation is:
    x2 dy/dx= y - xy
    IC (initial conditions): y(-1) = -1 (This is used to solve for C)
    Must first separate the variables x and y and then integrate them and solve for y, but I got stuck...

    x2dy = (y - xy)dx
    x2dy = y(1-x)dx
    dy= y(1-x)dx/x2 <-- not sure what to do with the y now... I figure I could divide everything by y so I could bring it to the left side but the right side would have dx/y

    The answer is y = e-(1+1/x)/x
     
    Last edited: Sep 25, 2011
  2. jcsd
  3. Sep 25, 2011 #2
    You are doing it right, but when you divide by Y you will have dy/y, and that is perfectly acceptable. The right side you will have (1-x)/x^2 dx. Then integrate both sides.
     
  4. Sep 25, 2011 #3
    But wouldn't the right side have dx/y? That's why i'm stuck, I'm not sure if it's acceptable!
     
  5. Sep 25, 2011 #4
    dx can be treated as just another factor on the right side. So since they are all factors when you divide by y the y just goes away on the right side.

    Now if it was y + (whatever)dx, then yes if you divided by y you would have a dx/y.
     
  6. Sep 25, 2011 #5
    Alright thank you Jackx
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook