Tenemos la indeterminación de tipo
oo/oo,
tal que el límite para el numerador es
$$\lim_{n \to \infty} \frac{1}{\sinh{\left(\frac{\pi}{n + 1} \right)}} = \infty$$
y el límite para el denominador es
$$\lim_{n \to \infty} \frac{1}{\sinh{\left(\frac{\pi}{n} \right)}} = \infty$$
Vamos a probar las derivadas del numerador y denominador hasta eliminar la indeterminación.
$$\lim_{n \to \infty}\left(\frac{\sinh{\left(\frac{\pi}{n} \right)}}{\sinh{\left(\frac{\pi}{n + 1} \right)}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{\frac{d}{d n} \frac{1}{\sinh{\left(\frac{\pi}{n + 1} \right)}}}{\frac{d}{d n} \frac{1}{\sinh{\left(\frac{\pi}{n} \right)}}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{n^{2} \sinh^{2}{\left(\frac{\pi}{n} \right)} \cosh{\left(\frac{\pi}{n + 1} \right)}}{\left(n + 1\right)^{2} \sinh^{2}{\left(\frac{\pi}{n + 1} \right)} \cosh{\left(\frac{\pi}{n} \right)}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{1}{\left(\frac{1}{\sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{2}{n \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{1}{n^{2} \sinh^{2}{\left(\frac{\pi}{n} \right)}}\right) \sinh^{2}{\left(\frac{\pi}{n + 1} \right)}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{\frac{d}{d n} \frac{1}{\sinh^{2}{\left(\frac{\pi}{n + 1} \right)}}}{\frac{d}{d n} \left(\frac{1}{\sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{2}{n \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{1}{n^{2} \sinh^{2}{\left(\frac{\pi}{n} \right)}}\right)}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{2 \pi \cosh{\left(\frac{\pi}{n + 1} \right)}}{\left(n + 1\right)^{2} \left(- \frac{2}{n^{2} \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{2 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{2} \sinh^{3}{\left(\frac{\pi}{n} \right)}} - \frac{2}{n^{3} \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{4 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{3} \sinh^{3}{\left(\frac{\pi}{n} \right)}} + \frac{2 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{4} \sinh^{3}{\left(\frac{\pi}{n} \right)}}\right) \sinh^{3}{\left(\frac{\pi}{n + 1} \right)}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{2 \pi}{\left(n + 1\right)^{2} \left(- \frac{2}{n^{2} \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{2 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{2} \sinh^{3}{\left(\frac{\pi}{n} \right)}} - \frac{2}{n^{3} \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{4 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{3} \sinh^{3}{\left(\frac{\pi}{n} \right)}} + \frac{2 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{4} \sinh^{3}{\left(\frac{\pi}{n} \right)}}\right) \sinh^{3}{\left(\frac{\pi}{n + 1} \right)}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{2 \pi}{\left(n + 1\right)^{2} \left(- \frac{2}{n^{2} \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{2 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{2} \sinh^{3}{\left(\frac{\pi}{n} \right)}} - \frac{2}{n^{3} \sinh^{2}{\left(\frac{\pi}{n} \right)}} + \frac{4 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{3} \sinh^{3}{\left(\frac{\pi}{n} \right)}} + \frac{2 \pi \cosh{\left(\frac{\pi}{n} \right)}}{n^{4} \sinh^{3}{\left(\frac{\pi}{n} \right)}}\right) \sinh^{3}{\left(\frac{\pi}{n + 1} \right)}}\right)$$
=
$$1$$
Como puedes ver, hemos aplicado el método de l'Hopital (utilizando la derivada del numerador y denominador) 2 vez (veces)