\frac{d}{dy}f_1(x,y) - \frac{d}{dx}f_2(x,y) = 4xy\ln{y} \\
v=xy \\
\frac{dv}{dx} = y \\
\frac{dv}{dy} = x \\
\varphi(xy) = \frac{A}{yf_2 - xf_1} \\
\frac{1}{\mu}\mu' = \frac{4xylny}{y(x-2x^2y\ln{y}-xy} = \frac{-2}{xy} = \frac{-2}{v} \\
\int{\frac{1}{\mu}d\mu}=-2\int{\frac{1}{v}dv}