Sr Examen

Límite de la función cot(t)*log(t*cot(t))

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Solución

Ha introducido [src]
 lim  (cot(t)*log(t*cot(t)))
   pi                       
t->--+                      
   2                        
$$\lim_{t \to \frac{\pi}{2}^+}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right)$$
Limit(cot(t)*log(t*cot(t)), t, pi/2)
Método de l'Hopital
Tenemos la indeterminación de tipo
0/0,

tal que el límite para el numerador es
$$\lim_{t \to \frac{\pi}{2}^+} \cot{\left(t \right)} = 0$$
y el límite para el denominador es
$$\lim_{t \to \frac{\pi}{2}^+} \frac{1}{\log{\left(t \cot{\left(t \right)} \right)}} = 0$$
Vamos a probar las derivadas del numerador y denominador hasta eliminar la indeterminación.
$$\lim_{t \to \frac{\pi}{2}^+}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right)$$
=
$$\lim_{t \to \frac{\pi}{2}^+}\left(\frac{\frac{d}{d t} \cot{\left(t \right)}}{\frac{d}{d t} \frac{1}{\log{\left(t \cot{\left(t \right)} \right)}}}\right)$$
=
$$\lim_{t \to \frac{\pi}{2}^+}\left(- \frac{t \left(- \cot^{2}{\left(t \right)} - 1\right) \log{\left(t \cot{\left(t \right)} \right)}^{2} \cot{\left(t \right)}}{t \left(- \cot^{2}{\left(t \right)} - 1\right) + \cot{\left(t \right)}}\right)$$
=
$$\lim_{t \to \frac{\pi}{2}^+}\left(\left(- \cot^{2}{\left(t \right)} - 1\right) \log{\left(t \cot{\left(t \right)} \right)}^{2} \cot{\left(t \right)}\right)$$
=
$$\lim_{t \to \frac{\pi}{2}^+}\left(\frac{\frac{d}{d t} \log{\left(t \cot{\left(t \right)} \right)}^{2} \cot{\left(t \right)}}{\frac{d}{d t} \frac{1}{- \cot^{2}{\left(t \right)} - 1}}\right)$$
=
$$\lim_{t \to \frac{\pi}{2}^+}\left(\frac{\left(\left(- \cot^{2}{\left(t \right)} - 1\right) \log{\left(t \cot{\left(t \right)} \right)}^{2} + \frac{2 \left(t \left(- \cot^{2}{\left(t \right)} - 1\right) + \cot{\left(t \right)}\right) \log{\left(t \cot{\left(t \right)} \right)}}{t}\right) \left(- \cot^{2}{\left(t \right)} - 1\right)^{2}}{\left(- 2 \cot^{2}{\left(t \right)} - 2\right) \cot{\left(t \right)}}\right)$$
=
$$\lim_{t \to \frac{\pi}{2}^+}\left(- \frac{- \log{\left(t \cot{\left(t \right)} \right)}^{2} \cot^{2}{\left(t \right)} - \log{\left(t \cot{\left(t \right)} \right)}^{2} - 2 \log{\left(t \cot{\left(t \right)} \right)} \cot^{2}{\left(t \right)} - 2 \log{\left(t \cot{\left(t \right)} \right)} + \frac{2 \log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}}{t}}{2 \cot{\left(t \right)}}\right)$$
=
$$\lim_{t \to \frac{\pi}{2}^+}\left(- \frac{- \log{\left(t \cot{\left(t \right)} \right)}^{2} \cot^{2}{\left(t \right)} - \log{\left(t \cot{\left(t \right)} \right)}^{2} - 2 \log{\left(t \cot{\left(t \right)} \right)} \cot^{2}{\left(t \right)} - 2 \log{\left(t \cot{\left(t \right)} \right)} + \frac{2 \log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}}{t}}{2 \cot{\left(t \right)}}\right)$$
=
$$0$$
Como puedes ver, hemos aplicado el método de l'Hopital (utilizando la derivada del numerador y denominador) 2 vez (veces)
Gráfica
Respuesta rápida [src]
0
$$0$$
A la izquierda y a la derecha [src]
 lim  (cot(t)*log(t*cot(t)))
   pi                       
t->--+                      
   2                        
$$\lim_{t \to \frac{\pi}{2}^+}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right)$$
0
$$0$$
= (0.00183324192022206 - 0.000852522131236593j)
 lim  (cot(t)*log(t*cot(t)))
   pi                       
t->---                      
   2                        
$$\lim_{t \to \frac{\pi}{2}^-}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right)$$
0
$$0$$
= -0.00191755035984963
= -0.00191755035984963
Otros límites con t→0, -oo, +oo, 1
$$\lim_{t \to \frac{\pi}{2}^-}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right) = 0$$
Más detalles con t→pi/2 a la izquierda
$$\lim_{t \to \frac{\pi}{2}^+}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right) = 0$$
$$\lim_{t \to \infty}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right)$$
Más detalles con t→oo
$$\lim_{t \to 0^-}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right) = 0$$
Más detalles con t→0 a la izquierda
$$\lim_{t \to 0^+}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right) = 0$$
Más detalles con t→0 a la derecha
$$\lim_{t \to 1^-}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right) = - \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\tan{\left(1 \right)}}$$
Más detalles con t→1 a la izquierda
$$\lim_{t \to 1^+}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right) = - \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\tan{\left(1 \right)}}$$
Más detalles con t→1 a la derecha
$$\lim_{t \to -\infty}\left(\log{\left(t \cot{\left(t \right)} \right)} \cot{\left(t \right)}\right)$$
Más detalles con t→-oo
Respuesta numérica [src]
(0.00183324192022206 - 0.000852522131236593j)
(0.00183324192022206 - 0.000852522131236593j)