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Límite de la función (cos(3*x)^2-cos(3*x)-6*x*cos(3*x)*sin(3*x))/(3*x*(6*x*cos(3*x)+sin(3*x)))

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Solución

Ha introducido [src]
     /   2                                        \
     |cos (3*x) - cos(3*x) - 6*x*cos(3*x)*sin(3*x)|
 lim |--------------------------------------------|
x->0+\       3*x*(6*x*cos(3*x) + sin(3*x))        /
$$\lim_{x \to 0^+}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
Limit((cos(3*x)^2 - cos(3*x) - (6*x)*cos(3*x)*sin(3*x))/(((3*x)*((6*x)*cos(3*x) + sin(3*x)))), x, 0)
Método de l'Hopital
Tenemos la indeterminación de tipo
0/0,

tal que el límite para el numerador es
$$\lim_{x \to 0^+}\left(\frac{\left(- 6 x \sin{\left(3 x \right)} + \cos{\left(3 x \right)} - 1\right) \cos{\left(3 x \right)}}{3 x}\right) = 0$$
y el límite para el denominador es
$$\lim_{x \to 0^+}\left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right) = 0$$
Vamos a probar las derivadas del numerador y denominador hasta eliminar la indeterminación.
$$\lim_{x \to 0^+}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
=
Introducimos una pequeña modificación de la función bajo el signo del límite
$$\lim_{x \to 0^+}\left(\frac{\left(- 6 x \sin{\left(3 x \right)} + \cos{\left(3 x \right)} - 1\right) \cos{\left(3 x \right)}}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{\frac{d}{d x} \frac{\left(- 6 x \sin{\left(3 x \right)} + \cos{\left(3 x \right)} - 1\right) \cos{\left(3 x \right)}}{3 x}}{\frac{d}{d x} \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{6 \sin^{2}{\left(3 x \right)} - 6 \cos^{2}{\left(3 x \right)} - \frac{2 \sin{\left(3 x \right)} \cos{\left(3 x \right)}}{x} + \frac{\sin{\left(3 x \right)}}{x} - \frac{\cos^{2}{\left(3 x \right)}}{3 x^{2}} + \frac{\cos{\left(3 x \right)}}{3 x^{2}}}{- 18 x \sin{\left(3 x \right)} + 9 \cos{\left(3 x \right)}}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{6 \sin^{2}{\left(3 x \right)} - 6 \cos^{2}{\left(3 x \right)} - \frac{2 \sin{\left(3 x \right)} \cos{\left(3 x \right)}}{x} + \frac{\sin{\left(3 x \right)}}{x} - \frac{\cos^{2}{\left(3 x \right)}}{3 x^{2}} + \frac{\cos{\left(3 x \right)}}{3 x^{2}}}{- 18 x \sin{\left(3 x \right)} + 9 \cos{\left(3 x \right)}}\right)$$
=
$$- \frac{5}{6}$$
Como puedes ver, hemos aplicado el método de l'Hopital (utilizando la derivada del numerador y denominador) 1 vez (veces)
Gráfica
A la izquierda y a la derecha [src]
     /   2                                        \
     |cos (3*x) - cos(3*x) - 6*x*cos(3*x)*sin(3*x)|
 lim |--------------------------------------------|
x->0+\       3*x*(6*x*cos(3*x) + sin(3*x))        /
$$\lim_{x \to 0^+}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
-5/6
$$- \frac{5}{6}$$
= -0.833333333333333
     /   2                                        \
     |cos (3*x) - cos(3*x) - 6*x*cos(3*x)*sin(3*x)|
 lim |--------------------------------------------|
x->0-\       3*x*(6*x*cos(3*x) + sin(3*x))        /
$$\lim_{x \to 0^-}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
-5/6
$$- \frac{5}{6}$$
= -0.833333333333333
= -0.833333333333333
Respuesta rápida [src]
-5/6
$$- \frac{5}{6}$$
Otros límites con x→0, -oo, +oo, 1
$$\lim_{x \to 0^-}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right) = - \frac{5}{6}$$
Más detalles con x→0 a la izquierda
$$\lim_{x \to 0^+}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right) = - \frac{5}{6}$$
$$\lim_{x \to \infty}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
Más detalles con x→oo
$$\lim_{x \to 1^-}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right) = \frac{- 6 \sin{\left(3 \right)} \cos{\left(3 \right)} + \cos^{2}{\left(3 \right)} - \cos{\left(3 \right)}}{18 \cos{\left(3 \right)} + 3 \sin{\left(3 \right)}}$$
Más detalles con x→1 a la izquierda
$$\lim_{x \to 1^+}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right) = \frac{- 6 \sin{\left(3 \right)} \cos{\left(3 \right)} + \cos^{2}{\left(3 \right)} - \cos{\left(3 \right)}}{18 \cos{\left(3 \right)} + 3 \sin{\left(3 \right)}}$$
Más detalles con x→1 a la derecha
$$\lim_{x \to -\infty}\left(\frac{- 6 x \cos{\left(3 x \right)} \sin{\left(3 x \right)} + \left(\cos^{2}{\left(3 x \right)} - \cos{\left(3 x \right)}\right)}{3 x \left(6 x \cos{\left(3 x \right)} + \sin{\left(3 x \right)}\right)}\right)$$
Más detalles con x→-oo
Respuesta numérica [src]
-0.833333333333333
-0.833333333333333