Integrating factor of the differential equation $\frac{d y}{d x}+y=\frac{x^3+y}{x}$ is

The degree of the differential equation $\left[1+\left(\frac{d y}{d x}\right)^2\right]^{\frac{3}{4}}=\left(\frac{d^2 y}{d x^2}\right)^{\frac{1}{3}}$

Which of the following transformations reduce the differential equation $\frac{d z}{d x}+\frac{z}{x} \log z=\frac{z}{x^2}(\log z)^2$ into the form $\frac{d u}{d x}+P(x) u=Q(x)$

Solution of the differential equation $y \frac{d y}{d x}+x=0$ represents a family of