Solution
= Solution
Separation of variables gives $\ln|y|=\sqrt{1+x^2}+C$ for a nonzero solution. Including the zero solution in the arbitrary real amplitude gives
$$
\boxed{y(x)=A\exp\sqrt{1+x^2},\qquad A\in\mathbb R.}
$$
Differentiating the exponent verifies the equation. This form keeps the zero solution that a division by $y$ could otherwise conceal.