# Linear 2nd order ODE?

1. Dec 28, 2009

### kyin01

1. The problem statement, all variables and given/known data
$$y''x^{2}$$ + 4xy' -y = ln(x)

3. The attempt at a solution
-I considered the quadratic characteristic equation, but it wont work because of the x^2
-I also tried variation of parameters.
so i have v = y' and v'=y'' but i have no idea what i would sub when I get to y.

any ideas?

2. Dec 28, 2009

### tiny-tim

Hi kyin01!

Try changing x

look for a u(x) such that the equation becomes something simple in dy/du and d2y/du2.

3. Dec 28, 2009

### yungman

I think the standard way is to first find the solutions of the assoc. homogeneous DE $$y''x^{2}$$ + 4xy' -y =0 using Cauchy Euler DE by letting $$y=x^{m}$$.

Then use variation of parameter etc. to find the particular solution.

4. Dec 29, 2009

### HallsofIvy

Staff Emeritus
Yes, although that can make the calculations pretty complicated. As tiny-time suggested, the substitution u= ln(x) will change any "Euler-type" or "Equipotential" equation to a very simple equation with constant coefficients.

I rather suspect that if kyin01 were to check his recent notes or textbook where this problem is given, he would find a discussion of "Euler-type" or "Equipotential" equations. (The name varies from text book to text book.)