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cos(3x+1)<=-sqrt(2)/2

cos(3x+1)<=-sqrt(2)/2 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
                   ___ 
                -\/ 2  
cos(3*x + 1) <= -------
                   2   
$$\cos{\left(3 x + 1 \right)} \leq \frac{\left(-1\right) \sqrt{2}}{2}$$
cos(3*x + 1) <= (-sqrt(2))/2
Solución detallada
Se da la desigualdad:
$$\cos{\left(3 x + 1 \right)} \leq \frac{\left(-1\right) \sqrt{2}}{2}$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$\cos{\left(3 x + 1 \right)} = \frac{\left(-1\right) \sqrt{2}}{2}$$
Resolvemos:
Tenemos la ecuación
$$\cos{\left(3 x + 1 \right)} = \frac{\left(-1\right) \sqrt{2}}{2}$$
es la ecuación trigonométrica más simple
Esta ecuación se reorganiza en
$$3 x + 1 = \pi n + \operatorname{acos}{\left(- \frac{\sqrt{2}}{2} \right)}$$
$$3 x + 1 = \pi n - \pi + \operatorname{acos}{\left(- \frac{\sqrt{2}}{2} \right)}$$
O
$$3 x + 1 = \pi n + \frac{3 \pi}{4}$$
$$3 x + 1 = \pi n - \frac{\pi}{4}$$
, donde n es cualquier número entero
Transportemos
$$1$$
al miembro derecho de la ecuación
con el signo opuesto, en total:
$$3 x = \pi n - 1 + \frac{3 \pi}{4}$$
$$3 x = \pi n - 1 - \frac{\pi}{4}$$
Dividamos ambos miembros de la ecuación obtenida en
$$3$$
$$x_{1} = \frac{\pi n}{3} - \frac{1}{3} + \frac{\pi}{4}$$
$$x_{2} = \frac{\pi n}{3} - \frac{1}{3} - \frac{\pi}{12}$$
$$x_{1} = \frac{\pi n}{3} - \frac{1}{3} + \frac{\pi}{4}$$
$$x_{2} = \frac{\pi n}{3} - \frac{1}{3} - \frac{\pi}{12}$$
Las raíces dadas
$$x_{1} = \frac{\pi n}{3} - \frac{1}{3} + \frac{\pi}{4}$$
$$x_{2} = \frac{\pi n}{3} - \frac{1}{3} - \frac{\pi}{12}$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} \leq x_{1}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$\left(\frac{\pi n}{3} - \frac{1}{3} + \frac{\pi}{4}\right) + - \frac{1}{10}$$
=
$$\frac{\pi n}{3} - \frac{13}{30} + \frac{\pi}{4}$$
lo sustituimos en la expresión
$$\cos{\left(3 x + 1 \right)} \leq \frac{\left(-1\right) \sqrt{2}}{2}$$
$$\cos{\left(3 \left(\frac{\pi n}{3} - \frac{13}{30} + \frac{\pi}{4}\right) + 1 \right)} \leq \frac{\left(-1\right) \sqrt{2}}{2}$$
                             ___ 
    /  3    pi       \    -\/ 2  
-sin|- -- + -- + pi*n| <= -------
    \  10   4        /       2   
                          

pero
                             ___ 
    /  3    pi       \    -\/ 2  
-sin|- -- + -- + pi*n| >= -------
    \  10   4        /       2   
                          

Entonces
$$x \leq \frac{\pi n}{3} - \frac{1}{3} + \frac{\pi}{4}$$
no se cumple
significa que una de las soluciones de nuestra ecuación será con:
$$x \geq \frac{\pi n}{3} - \frac{1}{3} + \frac{\pi}{4} \wedge x \leq \frac{\pi n}{3} - \frac{1}{3} - \frac{\pi}{12}$$
         _____  
        /     \  
-------•-------•-------
       x1      x2
Solución de la desigualdad en el gráfico
Respuesta rápida [src]
   /           /                                                         ___ /       2     \           \        /                                                         ___ /       2     \           \     \
   |           |                4*tan(1/2)                             \/ 2 *\1 + tan (1/2)/           |        |                4*tan(1/2)                             \/ 2 *\1 + tan (1/2)/           |     |
   |     2*atan|------------------------------------------ + ------------------------------------------|  2*atan|------------------------------------------ - ------------------------------------------|     |
   |           |       ___        2          ___    2               ___        2          ___    2     |        |       ___        2          ___    2               ___        2          ___    2     |     |
   |           \-2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)   -2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)/        \-2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)   -2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)/     |
And|x <= -----------------------------------------------------------------------------------------------, ----------------------------------------------------------------------------------------------- <= x|
   \                                                    3                                                                                                3                                                    /
$$x \leq \frac{2 \operatorname{atan}{\left(\frac{\sqrt{2} \left(\tan^{2}{\left(\frac{1}{2} \right)} + 1\right)}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} + \frac{4 \tan{\left(\frac{1}{2} \right)}}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} \right)}}{3} \wedge \frac{2 \operatorname{atan}{\left(- \frac{\sqrt{2} \left(\tan^{2}{\left(\frac{1}{2} \right)} + 1\right)}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} + \frac{4 \tan{\left(\frac{1}{2} \right)}}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} \right)}}{3} \leq x$$
(x <= 2*atan(4*tan(1/2)/(-2 + sqrt(2) + 2*tan(1/2)^2 + sqrt(2)*tan(1/2)^2) + sqrt(2)*(1 + tan(1/2)^2)/(-2 + sqrt(2) + 2*tan(1/2)^2 + sqrt(2)*tan(1/2)^2))/3)∧(2*atan(4*tan(1/2)/(-2 + sqrt(2) + 2*tan(1/2)^2 + sqrt(2)*tan(1/2)^2) - sqrt(2)*(1 + tan(1/2)^2)/(-2 + sqrt(2) + 2*tan(1/2)^2 + sqrt(2)*tan(1/2)^2))/3 <= x)
Respuesta rápida 2 [src]
       /                                                         ___ /       2     \           \        /                                                         ___ /       2     \           \ 
       |                4*tan(1/2)                             \/ 2 *\1 + tan (1/2)/           |        |                4*tan(1/2)                             \/ 2 *\1 + tan (1/2)/           | 
 2*atan|------------------------------------------ - ------------------------------------------|  2*atan|------------------------------------------ + ------------------------------------------| 
       |       ___        2          ___    2               ___        2          ___    2     |        |       ___        2          ___    2               ___        2          ___    2     | 
       \-2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)   -2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)/        \-2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)   -2 + \/ 2  + 2*tan (1/2) + \/ 2 *tan (1/2)/ 
[-----------------------------------------------------------------------------------------------, -----------------------------------------------------------------------------------------------]
                                                3                                                                                                3                                                
$$x\ in\ \left[\frac{2 \operatorname{atan}{\left(- \frac{\sqrt{2} \left(\tan^{2}{\left(\frac{1}{2} \right)} + 1\right)}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} + \frac{4 \tan{\left(\frac{1}{2} \right)}}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} \right)}}{3}, \frac{2 \operatorname{atan}{\left(\frac{\sqrt{2} \left(\tan^{2}{\left(\frac{1}{2} \right)} + 1\right)}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} + \frac{4 \tan{\left(\frac{1}{2} \right)}}{-2 + \sqrt{2} \tan^{2}{\left(\frac{1}{2} \right)} + 2 \tan^{2}{\left(\frac{1}{2} \right)} + \sqrt{2}} \right)}}{3}\right]$$
x in Interval(2*atan(-sqrt(2)*(tan(1/2)^2 + 1)/(-2 + sqrt(2)*tan(1/2)^2 + 2*tan(1/2)^2 + sqrt(2)) + 4*tan(1/2)/(-2 + sqrt(2)*tan(1/2)^2 + 2*tan(1/2)^2 + sqrt(2)))/3, 2*atan(sqrt(2)*(tan(1/2)^2 + 1)/(-2 + sqrt(2)*tan(1/2)^2 + 2*tan(1/2)^2 + sqrt(2)) + 4*tan(1/2)/(-2 + sqrt(2)*tan(1/2)^2 + 2*tan(1/2)^2 + sqrt(2)))/3)
Gráfico
cos(3x+1)<=-sqrt(2)/2 desigualdades