28. Solve the equation $2 y d y=3 x^{2} d x$.
Solution. Here $\varphi(y)=2 y, f(x)=3 x^{2}$. Integrating both sides of the equation, we have

$$
\int 2 y d y=\int 3 x^{2} d x, y^{2}=x^{3}+C
$$

We obtained the general solution of the differential equation. This solution can be written in explicit form: $y=\sqrt{x^{3}+C}$.