Let $\alpha|x|=|y| \mathrm{e}^{x y-\beta}, \alpha, \beta \in \mathbf{N}$ be the solution of the differential…
Let $\alpha|x|=|y| \mathrm{e}^{x y-\beta}, \alpha, \beta \in \mathbf{N}$ be the solution of the differential equation $x \mathrm{~d} y-y \mathrm{~d} x+x y(x \mathrm{~d} y+y \mathrm{~d} x)=0$, $y(1)=2$. Then $\alpha+\beta$ is equal to ________
Solution
$\begin{aligned}
& a|x|=|y| e^{y x-\beta}, a, b \in N \\
& x d y-y d x+x y(x d y+y d x)=0 \\
& \frac{d y}{y}-\frac{d x}{x}+(x d y+y d x)=0 \\
& \ell n|y|-\ell n|x|+x y=c \\
& y(1)=2 \\
& \ell n|2|-0+2=c \\
& c=2+\ell n 2 \\
& \ell n|y|-\ell n|x|+x y=2+\ell n 2 \\
& \ell n|x|=\ell n\left|\frac{y}{2}\right|-2+x y \\
& |x|=\left|\frac{y}{2}\right| e^{x y-2} \\
& 2|x|=|y| e^{x y-2} \\
& \alpha=2 \quad \beta=2 \quad \alpha+\beta=4
\end{aligned}$