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: Differential equation of dy/dx = (2x-y+4)/ (4x-2y +1)

  1. Feb 17, 2016 #1
    1. The problem statement, all variables and given/known data
    I'm asked to use the transformation of v= 2x-y to solve dy/dx = (2x-y+4)/ (4x-2y +1)

    the answer given is (2/9)(6x-3y-2) +(7/9)ln(6x-3y-2) = x +c , i got (2/9)(6x-3y) +(7/9)ln(6x-3y-2) = x +c , what's wrong with my working ?

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

    • 256.jpg
      File size:
      29.4 KB
  2. jcsd
  3. Feb 17, 2016 #2


    User Avatar
    2017 Award

    Staff: Mentor

    The two answers differ by a constant summand of 4/9. As you have "+c" anyway, this difference does not matter.
  4. Feb 18, 2016 #3
    lol , why the author wanna dd in another (2/9)(-2) into the answer ? this is confusing ...
  5. Feb 18, 2016 #4


    User Avatar
    Science Advisor

    Presumably, because the author used a different method to arrive at a solution. In any case, the point is that, because the derivative of a constant is 0, two functions, differing by a constant, can be solutions to the same first order differential equation.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted