Tomamos como el límite
$$\lim_{x \to 5^+}\left(\frac{x^{2} - 25}{\left(x^{3} - 5 x\right)^{2}}\right)$$
cambiamos
$$\lim_{x \to 5^+}\left(\frac{x^{2} - 25}{\left(x^{3} - 5 x\right)^{2}}\right)$$
=
$$\lim_{x \to 5^+}\left(\frac{\left(x - 5\right) \left(x + 5\right)}{x^{2} \left(x^{2} - 5\right)^{2}}\right)$$
=
$$\lim_{x \to 5^+}\left(\frac{\left(x - 5\right) \left(x + 5\right)}{x^{2} \left(x^{2} - 5\right)^{2}}\right) = $$
$$\frac{\left(-5 + 5\right) \left(5 + 5\right)}{25 \left(-5 + 5^{2}\right)^{2}} = $$
= 0
Entonces la respuesta definitiva es:
$$\lim_{x \to 5^+}\left(\frac{x^{2} - 25}{\left(x^{3} - 5 x\right)^{2}}\right) = 0$$