$$ y \frac{ dy }{ dx } = x $$
$$ y \ dy = x \ dx $$
$$ \int y \ dy = \int x \ dx $$
$$ \frac{ y^2 }{ 2 } + A = \frac{ x^2 }{ 2 } + B $$
$$ y^2 = x^2 + C $$
$$ y \frac{ dy }{ dx } = x $$
$$ y \ dy = x \ dx $$
$$ \int y \ dy = \int x \ dx $$
$$ \frac{ y^2 }{ 2 } + A = \frac{ x^2 }{ 2 } + B $$
$$ y^2 = x^2 + C $$