Concept:
To identify the family of curves represented by a differential equation, solve the differential equation and compare the obtained equation with standard forms of conics.
The given equation is
\[
3y\frac{dy}{dx}+2x=0
\]
Step 1: Separate the variables.
\[
3y\frac{dy}{dx}=-2x
\]
Multiply both sides by \(dx\):
\[
3y\,dy=-2x\,dx
\]
Step 2: Integrate both sides.
\[
\int 3y\,dy=\int -2x\,dx
\]
\[
\frac{3y^2}{2}=-x^2+C
\]
Step 3: Rearrange the equation.
\[
x^2+\frac{3y^2}{2}=C
\]
Multiplying by \(2\),
\[
2x^2+3y^2=C_1
\]
where \(C_1\) is a constant.
Step 4: Compare with standard conic.
The equation
\[
2x^2+3y^2=C_1
\]
contains positive coefficients of both \(x^2\) and \(y^2\).
This represents an ellipse.
Step 5: Final answer.
\[
\boxed{\text{Ellipse}}
\]