Second Order ODE/y'' - x f(x) y' + f(x) y = 0

Theorem
The second order ODE:
 * $(1): \quad y'' - x \, \map f x y' + \map f x y = 0$

has the general solution:
 * $\ds y = C_1 x + C_2 x \int x^{-2} e^{\int x \, \map f x \rd x} \rd x$

Proof
Note that:

Substituting into $(1)$:

and so it has been demonstrated that:
 * $y_1 = x$

is a particular solution of $(1)$.

$(1)$ is in the form:
 * $y'' + \map P x y' + \map Q x y = 0$

where:
 * $\map P x = -x \map f x$

From Particular Solution to Homogeneous Linear Second Order ODE gives rise to Another:
 * $\map {y_2} x = \map v x \map {y_1} x$

where:
 * $\ds v = \int \dfrac 1 { {y_1}^2} e^{-\int P \rd x} \rd x$

is also a particular solution of $(1)$.

We have that:

Hence:

and so:

From Two Linearly Independent Solutions of Homogeneous Linear Second Order ODE generate General Solution:


 * $\ds y = C_1 x + C_2 x \int x^{-2} e^{\int x \map f x \rd x} \rd x$