Solution of differential equation
\[
x^2-1+\left(\frac{x}{y}\right)^{-1}\frac{dy}{dx}
+\frac{x^2}{2!}\left(\frac{dy}{dx}\right)^2
+\frac{x^3}{3!}\left(\frac{dy}{dx}\right)^3+\cdots=0
\]
is
Show Hint
Identify known series expansions to simplify differential equations.