Tenemos la indeterminación de tipo
oo/oo,
tal que el límite para el numerador es
$$\lim_{x \to \infty} \operatorname{atan}^{- x}{\left(\frac{\pi}{3 x} \right)} = \infty$$
y el límite para el denominador es
$$\lim_{x \to \infty} \operatorname{atan}^{- x - 1}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} = \infty$$
Vamos a probar las derivadas del numerador y denominador hasta eliminar la indeterminación.
$$\lim_{x \to \infty}\left(\operatorname{atan}^{- x}{\left(\frac{\pi}{3 x} \right)} \operatorname{atan}^{x + 1}{\left(\frac{\pi}{3 x + 3} \right)}\right)$$
=
Introducimos una pequeña modificación de la función bajo el signo del límite
$$\lim_{x \to \infty}\left(\operatorname{atan}^{- x}{\left(\frac{\pi}{3 x} \right)} \operatorname{atan}^{x + 1}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{\frac{d}{d x} \operatorname{atan}^{- x}{\left(\frac{\pi}{3 x} \right)}}{\frac{d}{d x} \operatorname{atan}^{- x - 1}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{\left(- \log{\left(\operatorname{atan}{\left(\frac{\pi}{3 x} \right)} \right)} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} \operatorname{atan}^{x}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} \operatorname{atan}^{x}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 x \operatorname{atan}{\left(\frac{\pi}{3 x} \right)} + \frac{\pi^{2} \operatorname{atan}{\left(\frac{\pi}{3 x} \right)}}{3 x}}\right) \operatorname{atan}^{- x}{\left(\frac{\pi}{3 x} \right)}}{\frac{\pi x}{3 x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 6 x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{2 \pi^{2} x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 3 \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)}} - \log{\left(\operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} \right)} + \frac{\pi}{3 x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 6 x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{2 \pi^{2} x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 3 \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)}}}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{\left(- \log{\left(\operatorname{atan}{\left(\frac{\pi}{3 x} \right)} \right)} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} \operatorname{atan}^{x}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} \operatorname{atan}^{x}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 x \operatorname{atan}{\left(\frac{\pi}{3 x} \right)} + \frac{\pi^{2} \operatorname{atan}{\left(\frac{\pi}{3 x} \right)}}{3 x}}\right) \operatorname{atan}^{- x}{\left(\frac{\pi}{3 x} \right)}}{\frac{\pi x}{3 x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 6 x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{2 \pi^{2} x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 3 \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)}} - \log{\left(\operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} \right)} + \frac{\pi}{3 x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} x^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 6 x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{2 \pi^{2} x \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)} + 3 \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)} + \frac{\pi^{2} \operatorname{atan}{\left(\frac{\pi}{3 \left(x + 1\right)} \right)}}{3 \left(x^{2} + 2 x + 1\right)}}}\right)$$
=
$$0$$
Como puedes ver, hemos aplicado el método de l'Hopital (utilizando la derivada del numerador y denominador) 1 vez (veces)