Tomamos como el límite
$$\lim_{x \to 0^+}\left(\frac{3 x^{3} + x^{2}}{3 x^{3} + \left(x^{4} - 2 x^{2}\right)}\right)$$
cambiamos
$$\lim_{x \to 0^+}\left(\frac{3 x^{3} + x^{2}}{3 x^{3} + \left(x^{4} - 2 x^{2}\right)}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{x^{2} \left(3 x + 1\right)}{x^{2} \left(x^{2} + 3 x - 2\right)}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{3 x + 1}{x^{2} + 3 x - 2}\right) = $$
$$\frac{0 \cdot 3 + 1}{-2 + 0^{2} + 0 \cdot 3} = $$
= -1/2
Entonces la respuesta definitiva es:
$$\lim_{x \to 0^+}\left(\frac{3 x^{3} + x^{2}}{3 x^{3} + \left(x^{4} - 2 x^{2}\right)}\right) = - \frac{1}{2}$$