Tenemos la indeterminación de tipo
oo/-oo, tal que el límite para el numerador es
lim x → ∞ x = ∞ \lim_{x \to \infty} x = \infty x → ∞ lim x = ∞ y el límite para el denominador es
lim x → ∞ 1 log ( 2 atan ( x ) π ) = − ∞ \lim_{x \to \infty} \frac{1}{\log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}} = -\infty x → ∞ lim log ( π 2 atan ( x ) ) 1 = − ∞ Vamos a probar las derivadas del numerador y denominador hasta eliminar la indeterminación.
lim x → ∞ ( x log ( 2 atan ( x ) π ) ) \lim_{x \to \infty}\left(x \log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}\right) x → ∞ lim ( x log ( π 2 atan ( x ) ) ) =
Introducimos una pequeña modificación de la función bajo el signo del límite
lim x → ∞ ( x log ( 2 atan ( x ) π ) ) \lim_{x \to \infty}\left(x \log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}\right) x → ∞ lim ( x log ( π 2 atan ( x ) ) ) =
lim x → ∞ ( d d x x d d x 1 log ( 2 atan ( x ) π ) ) \lim_{x \to \infty}\left(\frac{\frac{d}{d x} x}{\frac{d}{d x} \frac{1}{\log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}}}\right) x → ∞ lim d x d l o g ( π 2 atan ( x ) ) 1 d x d x =
lim x → ∞ ( − ( x 2 + 1 ) log ( 2 atan ( x ) π ) 2 atan ( x ) ) \lim_{x \to \infty}\left(- \left(x^{2} + 1\right) \log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}^{2} \operatorname{atan}{\left(x \right)}\right) x → ∞ lim ( − ( x 2 + 1 ) log ( π 2 atan ( x ) ) 2 atan ( x ) ) =
lim x → ∞ ( − π ( x 2 + 1 ) log ( 2 atan ( x ) π ) 2 2 ) \lim_{x \to \infty}\left(- \frac{\pi \left(x^{2} + 1\right) \log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}^{2}}{2}\right) x → ∞ lim − 2 π ( x 2 + 1 ) log ( π 2 atan ( x ) ) 2 =
lim x → ∞ ( d d x ( − π ( x 2 + 1 ) 2 ) d d x 1 log ( 2 atan ( x ) π ) 2 ) \lim_{x \to \infty}\left(\frac{\frac{d}{d x} \left(- \frac{\pi \left(x^{2} + 1\right)}{2}\right)}{\frac{d}{d x} \frac{1}{\log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}^{2}}}\right) x → ∞ lim d x d l o g ( π 2 atan ( x ) ) 2 1 d x d ( − 2 π ( x 2 + 1 ) ) =
lim x → ∞ ( π x ( x 2 + 1 ) log ( 2 atan ( x ) π ) 3 atan ( x ) 2 ) \lim_{x \to \infty}\left(\frac{\pi x \left(x^{2} + 1\right) \log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}^{3} \operatorname{atan}{\left(x \right)}}{2}\right) x → ∞ lim 2 π x ( x 2 + 1 ) log ( π 2 atan ( x ) ) 3 atan ( x ) =
lim x → ∞ ( π 2 x ( x 2 + 1 ) log ( 2 atan ( x ) π ) 3 4 ) \lim_{x \to \infty}\left(\frac{\pi^{2} x \left(x^{2} + 1\right) \log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}^{3}}{4}\right) x → ∞ lim 4 π 2 x ( x 2 + 1 ) log ( π 2 atan ( x ) ) 3 =
lim x → ∞ ( d d x π 2 x ( x 2 + 1 ) 4 d d x 1 log ( 2 atan ( x ) π ) 3 ) \lim_{x \to \infty}\left(\frac{\frac{d}{d x} \frac{\pi^{2} x \left(x^{2} + 1\right)}{4}}{\frac{d}{d x} \frac{1}{\log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}^{3}}}\right) x → ∞ lim d x d l o g ( π 2 atan ( x ) ) 3 1 d x d 4 π 2 x ( x 2 + 1 ) =
lim x → ∞ ( − ( x 2 + 1 ) ( π 2 x 2 2 + π 2 ( x 2 + 1 ) 4 ) log ( 2 atan ( x ) π ) 4 atan ( x ) 3 ) \lim_{x \to \infty}\left(- \frac{\left(x^{2} + 1\right) \left(\frac{\pi^{2} x^{2}}{2} + \frac{\pi^{2} \left(x^{2} + 1\right)}{4}\right) \log{\left(\frac{2 \operatorname{atan}{\left(x \right)}}{\pi} \right)}^{4} \operatorname{atan}{\left(x \right)}}{3}\right) x → ∞ lim − 3 ( x 2 + 1 ) ( 2 π 2 x 2 + 4 π 2 ( x 2 + 1 ) ) log ( π 2 atan ( x ) ) 4 atan ( x ) =
lim x → ∞ ( ( 3 π 2 x 2 4 + π 2 4 ) ( − π x 2 log ( atan ( x ) ) 4 6 − 2 π x 2 log ( 2 ) log ( atan ( x ) ) 3 3 + 2 π x 2 log ( π ) log ( atan ( x ) ) 3 3 − π x 2 log ( π ) 2 log ( atan ( x ) ) 2 − π x 2 log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π x 2 log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π x 2 log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 2 π x 2 log ( 2 ) 3 log ( atan ( x ) ) 3 + 2 π x 2 log ( π ) 3 log ( atan ( x ) ) 3 + 2 π x 2 log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π x 2 log ( 2 ) 2 log ( π ) 2 − π x 2 log ( π ) 4 6 − π x 2 log ( 2 ) 4 6 + 2 π x 2 log ( 2 ) 3 log ( π ) 3 + 2 π x 2 log ( 2 ) log ( π ) 3 3 − π log ( atan ( x ) ) 4 6 − 2 π log ( 2 ) log ( atan ( x ) ) 3 3 + 2 π log ( π ) log ( atan ( x ) ) 3 3 − π log ( π ) 2 log ( atan ( x ) ) 2 − π log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 2 π log ( 2 ) 3 log ( atan ( x ) ) 3 + 2 π log ( π ) 3 log ( atan ( x ) ) 3 + 2 π log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π log ( 2 ) 2 log ( π ) 2 − π log ( π ) 4 6 − π log ( 2 ) 4 6 + 2 π log ( 2 ) 3 log ( π ) 3 + 2 π log ( 2 ) log ( π ) 3 3 ) ) \lim_{x \to \infty}\left(\left(\frac{3 \pi^{2} x^{2}}{4} + \frac{\pi^{2}}{4}\right) \left(- \frac{\pi x^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{4}}{6} - \frac{2 \pi x^{2} \log{\left(2 \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} + \frac{2 \pi x^{2} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} - \pi x^{2} \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - \pi x^{2} \log{\left(2 \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} + 2 \pi x^{2} \log{\left(2 \right)} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - 2 \pi x^{2} \log{\left(2 \right)} \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \frac{2 \pi x^{2} \log{\left(2 \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + \frac{2 \pi x^{2} \log{\left(\pi \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + 2 \pi x^{2} \log{\left(2 \right)}^{2} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \pi x^{2} \log{\left(2 \right)}^{2} \log{\left(\pi \right)}^{2} - \frac{\pi x^{2} \log{\left(\pi \right)}^{4}}{6} - \frac{\pi x^{2} \log{\left(2 \right)}^{4}}{6} + \frac{2 \pi x^{2} \log{\left(2 \right)}^{3} \log{\left(\pi \right)}}{3} + \frac{2 \pi x^{2} \log{\left(2 \right)} \log{\left(\pi \right)}^{3}}{3} - \frac{\pi \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{4}}{6} - \frac{2 \pi \log{\left(2 \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} + \frac{2 \pi \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} - \pi \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - \pi \log{\left(2 \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} + 2 \pi \log{\left(2 \right)} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - 2 \pi \log{\left(2 \right)} \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \frac{2 \pi \log{\left(2 \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + \frac{2 \pi \log{\left(\pi \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + 2 \pi \log{\left(2 \right)}^{2} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \pi \log{\left(2 \right)}^{2} \log{\left(\pi \right)}^{2} - \frac{\pi \log{\left(\pi \right)}^{4}}{6} - \frac{\pi \log{\left(2 \right)}^{4}}{6} + \frac{2 \pi \log{\left(2 \right)}^{3} \log{\left(\pi \right)}}{3} + \frac{2 \pi \log{\left(2 \right)} \log{\left(\pi \right)}^{3}}{3}\right)\right) x → ∞ lim ( ( 4 3 π 2 x 2 + 4 π 2 ) ( − 6 π x 2 log ( atan ( x ) ) 4 − 3 2 π x 2 log ( 2 ) log ( atan ( x ) ) 3 + 3 2 π x 2 log ( π ) log ( atan ( x ) ) 3 − π x 2 log ( π ) 2 log ( atan ( x ) ) 2 − π x 2 log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π x 2 log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π x 2 log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 3 2 π x 2 log ( 2 ) 3 log ( atan ( x ) ) + 3 2 π x 2 log ( π ) 3 log ( atan ( x ) ) + 2 π x 2 log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π x 2 log ( 2 ) 2 log ( π ) 2 − 6 π x 2 log ( π ) 4 − 6 π x 2 log ( 2 ) 4 + 3 2 π x 2 log ( 2 ) 3 log ( π ) + 3 2 π x 2 log ( 2 ) log ( π ) 3 − 6 π log ( atan ( x ) ) 4 − 3 2 π log ( 2 ) log ( atan ( x ) ) 3 + 3 2 π log ( π ) log ( atan ( x ) ) 3 − π log ( π ) 2 log ( atan ( x ) ) 2 − π log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 3 2 π log ( 2 ) 3 log ( atan ( x ) ) + 3 2 π log ( π ) 3 log ( atan ( x ) ) + 2 π log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π log ( 2 ) 2 log ( π ) 2 − 6 π log ( π ) 4 − 6 π log ( 2 ) 4 + 3 2 π log ( 2 ) 3 log ( π ) + 3 2 π log ( 2 ) log ( π ) 3 ) ) =
lim x → ∞ ( ( 3 π 2 x 2 4 + π 2 4 ) ( − π x 2 log ( atan ( x ) ) 4 6 − 2 π x 2 log ( 2 ) log ( atan ( x ) ) 3 3 + 2 π x 2 log ( π ) log ( atan ( x ) ) 3 3 − π x 2 log ( π ) 2 log ( atan ( x ) ) 2 − π x 2 log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π x 2 log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π x 2 log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 2 π x 2 log ( 2 ) 3 log ( atan ( x ) ) 3 + 2 π x 2 log ( π ) 3 log ( atan ( x ) ) 3 + 2 π x 2 log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π x 2 log ( 2 ) 2 log ( π ) 2 − π x 2 log ( π ) 4 6 − π x 2 log ( 2 ) 4 6 + 2 π x 2 log ( 2 ) 3 log ( π ) 3 + 2 π x 2 log ( 2 ) log ( π ) 3 3 − π log ( atan ( x ) ) 4 6 − 2 π log ( 2 ) log ( atan ( x ) ) 3 3 + 2 π log ( π ) log ( atan ( x ) ) 3 3 − π log ( π ) 2 log ( atan ( x ) ) 2 − π log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 2 π log ( 2 ) 3 log ( atan ( x ) ) 3 + 2 π log ( π ) 3 log ( atan ( x ) ) 3 + 2 π log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π log ( 2 ) 2 log ( π ) 2 − π log ( π ) 4 6 − π log ( 2 ) 4 6 + 2 π log ( 2 ) 3 log ( π ) 3 + 2 π log ( 2 ) log ( π ) 3 3 ) ) \lim_{x \to \infty}\left(\left(\frac{3 \pi^{2} x^{2}}{4} + \frac{\pi^{2}}{4}\right) \left(- \frac{\pi x^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{4}}{6} - \frac{2 \pi x^{2} \log{\left(2 \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} + \frac{2 \pi x^{2} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} - \pi x^{2} \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - \pi x^{2} \log{\left(2 \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} + 2 \pi x^{2} \log{\left(2 \right)} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - 2 \pi x^{2} \log{\left(2 \right)} \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \frac{2 \pi x^{2} \log{\left(2 \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + \frac{2 \pi x^{2} \log{\left(\pi \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + 2 \pi x^{2} \log{\left(2 \right)}^{2} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \pi x^{2} \log{\left(2 \right)}^{2} \log{\left(\pi \right)}^{2} - \frac{\pi x^{2} \log{\left(\pi \right)}^{4}}{6} - \frac{\pi x^{2} \log{\left(2 \right)}^{4}}{6} + \frac{2 \pi x^{2} \log{\left(2 \right)}^{3} \log{\left(\pi \right)}}{3} + \frac{2 \pi x^{2} \log{\left(2 \right)} \log{\left(\pi \right)}^{3}}{3} - \frac{\pi \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{4}}{6} - \frac{2 \pi \log{\left(2 \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} + \frac{2 \pi \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{3}}{3} - \pi \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - \pi \log{\left(2 \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} + 2 \pi \log{\left(2 \right)} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)}^{2} - 2 \pi \log{\left(2 \right)} \log{\left(\pi \right)}^{2} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \frac{2 \pi \log{\left(2 \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + \frac{2 \pi \log{\left(\pi \right)}^{3} \log{\left(\operatorname{atan}{\left(x \right)} \right)}}{3} + 2 \pi \log{\left(2 \right)}^{2} \log{\left(\pi \right)} \log{\left(\operatorname{atan}{\left(x \right)} \right)} - \pi \log{\left(2 \right)}^{2} \log{\left(\pi \right)}^{2} - \frac{\pi \log{\left(\pi \right)}^{4}}{6} - \frac{\pi \log{\left(2 \right)}^{4}}{6} + \frac{2 \pi \log{\left(2 \right)}^{3} \log{\left(\pi \right)}}{3} + \frac{2 \pi \log{\left(2 \right)} \log{\left(\pi \right)}^{3}}{3}\right)\right) x → ∞ lim ( ( 4 3 π 2 x 2 + 4 π 2 ) ( − 6 π x 2 log ( atan ( x ) ) 4 − 3 2 π x 2 log ( 2 ) log ( atan ( x ) ) 3 + 3 2 π x 2 log ( π ) log ( atan ( x ) ) 3 − π x 2 log ( π ) 2 log ( atan ( x ) ) 2 − π x 2 log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π x 2 log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π x 2 log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 3 2 π x 2 log ( 2 ) 3 log ( atan ( x ) ) + 3 2 π x 2 log ( π ) 3 log ( atan ( x ) ) + 2 π x 2 log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π x 2 log ( 2 ) 2 log ( π ) 2 − 6 π x 2 log ( π ) 4 − 6 π x 2 log ( 2 ) 4 + 3 2 π x 2 log ( 2 ) 3 log ( π ) + 3 2 π x 2 log ( 2 ) log ( π ) 3 − 6 π log ( atan ( x ) ) 4 − 3 2 π log ( 2 ) log ( atan ( x ) ) 3 + 3 2 π log ( π ) log ( atan ( x ) ) 3 − π log ( π ) 2 log ( atan ( x ) ) 2 − π log ( 2 ) 2 log ( atan ( x ) ) 2 + 2 π log ( 2 ) log ( π ) log ( atan ( x ) ) 2 − 2 π log ( 2 ) log ( π ) 2 log ( atan ( x ) ) − 3 2 π log ( 2 ) 3 log ( atan ( x ) ) + 3 2 π log ( π ) 3 log ( atan ( x ) ) + 2 π log ( 2 ) 2 log ( π ) log ( atan ( x ) ) − π log ( 2 ) 2 log ( π ) 2 − 6 π log ( π ) 4 − 6 π log ( 2 ) 4 + 3 2 π log ( 2 ) 3 log ( π ) + 3 2 π log ( 2 ) log ( π ) 3 ) ) =
− 2 π - \frac{2}{\pi} − π 2 Como puedes ver, hemos aplicado el método de l'Hopital (utilizando la derivada del numerador y denominador) 3 vez (veces)