Given the equation:
$$\frac{d}{d x} y{\left(x \right)} - \frac{x^{2} + 3 y^{2}{\left(x \right)}}{2 x y{\left(x \right)}} = 0$$
Do replacement
$$u{\left(x \right)} = \frac{y{\left(x \right)}}{x}$$
and because
$$y{\left(x \right)} = x u{\left(x \right)}$$
then
$$\frac{d}{d x} y{\left(x \right)} = x \frac{d}{d x} u{\left(x \right)} + u{\left(x \right)}$$
substitute
$$- \frac{3 u{\left(x \right)}}{2} + \frac{d}{d x} x u{\left(x \right)} - \frac{1}{2 u{\left(x \right)}} = 0$$
or
$$x \frac{d}{d x} u{\left(x \right)} - \frac{u{\left(x \right)}}{2} - \frac{1}{2 u{\left(x \right)}} = 0$$
This differential equation has the form:
$$f_1(x)*g_1(u)*u' = f_2(x)*g_2(u)$$
where
$$f_{1}{\left(x \right)} = 1$$
$$g_{1}{\left(u \right)} = 1$$
$$f_{2}{\left(x \right)} = - \frac{1}{x}$$
$$g_{2}{\left(u \right)} = - \frac{u^{2}{\left(x \right)} + 1}{2 u{\left(x \right)}}$$
We give the equation to the form:
$$\frac{g_1(u)}{g_2(u)}*u'= \frac{f_2(x)}{f_1(x)}$$
Divide both parts of the equation by g_2(u)
$$- \frac{u^{2}{\left(x \right)} + 1}{2 u{\left(x \right)}}$$
we get
$$- \frac{2 u{\left(x \right)} \frac{d}{d x} u{\left(x \right)}}{u^{2}{\left(x \right)} + 1} = - \frac{1}{x}$$
We separated the variables x and u.
Now, multiply the both equation sides by dx,
then the equation will be the
$$- \frac{2 dx u{\left(x \right)} \frac{d}{d x} u{\left(x \right)}}{u^{2}{\left(x \right)} + 1} = - \frac{dx}{x}$$
or
$$- \frac{2 du u{\left(x \right)}}{u^{2}{\left(x \right)} + 1} = - \frac{dx}{x}$$
Take the integrals from the both equation sides:
- the integral of the left side by u,
- the integral of the right side by x.
$$\int \left(- \frac{2 u}{u^{2} + 1}\right)\, du = \int \left(- \frac{1}{x}\right)\, dx$$
Detailed solution of the integral with uDetailed solution of the integral with xTake this integrals
$$- \log{\left(u^{2} + 1 \right)} = Const - \log{\left(x \right)}$$
Detailed solution of the equationWe get the simple equation with the unknown variable u.
(Const - it is a constant)
Solution is:
$$u_{1} = u{\left(x \right)} = - \sqrt{C_{1} x - 1}$$
$$u_{2} = u{\left(x \right)} = \sqrt{C_{1} x - 1}$$
do backward replacement
$$y{\left(x \right)} = x u{\left(x \right)}$$
$$y_{1} = y{\left(x \right)} = - x \sqrt{C_{1} x - 1}$$
$$y_{2} = y{\left(x \right)} = x \sqrt{C_{1} x - 1}$$