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sin^2x-3sinxcosx+cos^2x<0 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
   2                           2       
sin (x) - 3*sin(x)*cos(x) + cos (x) < 0
$$\left(\sin^{2}{\left(x \right)} - 3 \sin{\left(x \right)} \cos{\left(x \right)}\right) + \cos^{2}{\left(x \right)} < 0$$
sin(x)^2 - 3*sin(x)*cos(x) + cos(x)^2 < 0
Solución detallada
Se da la desigualdad:
$$\left(\sin^{2}{\left(x \right)} - 3 \sin{\left(x \right)} \cos{\left(x \right)}\right) + \cos^{2}{\left(x \right)} < 0$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$\left(\sin^{2}{\left(x \right)} - 3 \sin{\left(x \right)} \cos{\left(x \right)}\right) + \cos^{2}{\left(x \right)} = 0$$
Resolvemos:
$$x_{1} = 2 \operatorname{atan}{\left(- \frac{3}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{\sqrt{5}}{2} \right)}$$
$$x_{2} = - 2 \operatorname{atan}{\left(- \frac{\sqrt{5}}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{3}{2} \right)}$$
$$x_{3} = - 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)}$$
$$x_{4} = - 2 \operatorname{atan}{\left(- \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} + \frac{\sqrt{5}}{2} + \frac{3}{2} \right)}$$
$$x_{1} = 2 \operatorname{atan}{\left(- \frac{3}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{\sqrt{5}}{2} \right)}$$
$$x_{2} = - 2 \operatorname{atan}{\left(- \frac{\sqrt{5}}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{3}{2} \right)}$$
$$x_{3} = - 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)}$$
$$x_{4} = - 2 \operatorname{atan}{\left(- \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} + \frac{\sqrt{5}}{2} + \frac{3}{2} \right)}$$
Las raíces dadas
$$x_{3} = - 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)}$$
$$x_{2} = - 2 \operatorname{atan}{\left(- \frac{\sqrt{5}}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{3}{2} \right)}$$
$$x_{4} = - 2 \operatorname{atan}{\left(- \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} + \frac{\sqrt{5}}{2} + \frac{3}{2} \right)}$$
$$x_{1} = 2 \operatorname{atan}{\left(- \frac{3}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{\sqrt{5}}{2} \right)}$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} < x_{3}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{3} - \frac{1}{10}$$
=
$$- 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} - \frac{1}{10}$$
=
$$- 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} - \frac{1}{10}$$
lo sustituimos en la expresión
$$\left(\sin^{2}{\left(x \right)} - 3 \sin{\left(x \right)} \cos{\left(x \right)}\right) + \cos^{2}{\left(x \right)} < 0$$
$$\left(- 3 \sin{\left(- 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} - \frac{1}{10} \right)} \cos{\left(- 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} - \frac{1}{10} \right)} + \sin^{2}{\left(- 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} - \frac{1}{10} \right)}\right) + \cos^{2}{\left(- 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} - \frac{1}{10} \right)} < 0$$
    /           /                     ___________\\       /           /                     ___________\\        /           /                     ___________\\    /           /                     ___________\\    
    |           |      ___     ___   /       ___ ||       |           |      ___     ___   /       ___ ||        |           |      ___     ___   /       ___ ||    |           |      ___     ___   /       ___ ||    
   2|1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  ||      2|1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  ||        |1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  ||    |1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  || < 0
cos |-- + 2*atan|- + ----- + --------------------|| + sin |-- + 2*atan|- + ----- + --------------------|| + 3*cos|-- + 2*atan|- + ----- + --------------------||*sin|-- + 2*atan|- + ----- + --------------------||    
    \10         \2     2              2          //       \10         \2     2              2          //        \10         \2     2              2          //    \10         \2     2              2          //    

pero
    /           /                     ___________\\       /           /                     ___________\\        /           /                     ___________\\    /           /                     ___________\\    
    |           |      ___     ___   /       ___ ||       |           |      ___     ___   /       ___ ||        |           |      ___     ___   /       ___ ||    |           |      ___     ___   /       ___ ||    
   2|1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  ||      2|1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  ||        |1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  ||    |1          |3   \/ 5    \/ 6 *\/  3 + \/ 5  || > 0
cos |-- + 2*atan|- + ----- + --------------------|| + sin |-- + 2*atan|- + ----- + --------------------|| + 3*cos|-- + 2*atan|- + ----- + --------------------||*sin|-- + 2*atan|- + ----- + --------------------||    
    \10         \2     2              2          //       \10         \2     2              2          //        \10         \2     2              2          //    \10         \2     2              2          //    

Entonces
$$x < - 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)}$$
no se cumple
significa que una de las soluciones de nuestra ecuación será con:
$$x > - 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} \wedge x < - 2 \operatorname{atan}{\left(- \frac{\sqrt{5}}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{3}{2} \right)}$$
         _____           _____  
        /     \         /     \  
-------ο-------ο-------ο-------ο-------
       x3      x2      x4      x1

Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x > - 2 \operatorname{atan}{\left(\frac{\sqrt{5}}{2} + \frac{3}{2} + \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} \right)} \wedge x < - 2 \operatorname{atan}{\left(- \frac{\sqrt{5}}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{3}{2} \right)}$$
$$x > - 2 \operatorname{atan}{\left(- \frac{\sqrt{6} \sqrt{\sqrt{5} + 3}}{2} + \frac{\sqrt{5}}{2} + \frac{3}{2} \right)} \wedge x < 2 \operatorname{atan}{\left(- \frac{3}{2} + \frac{\sqrt{6} \sqrt{3 - \sqrt{5}}}{2} + \frac{\sqrt{5}}{2} \right)}$$
Solución de la desigualdad en el gráfico
Respuesta rápida [src]
   /       /      /   /    /    ___\\\                                                          \     /      /   /    /    ___\\\                                                          \    \
   |       |      |   |    |2*\/ 5 |||      /       ___________________________________________\|     |      |   |    |2*\/ 5 |||      /       ___________________________________________\|    |
   |       |      |   |atan|-------|||      |      /     /    /    ___\\       /    /    ___\\ ||     |      |   |atan|-------|||      |      /     /    /    ___\\       /    /    ___\\ ||    |
   |       |      |   |    \   5   /||      |     /      |    |2*\/ 5 ||       |    |2*\/ 5 || ||     |      |   |    \   5   /||      |     /      |    |2*\/ 5 ||       |    |2*\/ 5 || ||    |
   |       |      |cos|-------------||      |    /       |atan|-------||       |atan|-------|| ||     |      |sin|-------------||      |    /       |atan|-------||       |atan|-------|| ||    |
   |       |      |   \      2      /|      |   /       2|    \   5   /|      2|    \   5   /| ||     |      |   \      2      /|      |   /       2|    \   5   /|      2|    \   5   /| ||    |
And|x < -I*|I*atan|------------------| + log|  /     cos |-------------| + sin |-------------| ||, -I*|I*atan|------------------| + log|  /     cos |-------------| + sin |-------------| || < x|
   |       |      |   /    /    ___\\|      \\/          \      2      /       \      2      / /|     |      |   /    /    ___\\|      \\/          \      2      /       \      2      / /|    |
   |       |      |   |    |2*\/ 5 |||                                                          |     |      |   |    |2*\/ 5 |||                                                          |    |
   |       |      |   |atan|-------|||                                                          |     |      |   |atan|-------|||                                                          |    |
   |       |      |   |    \   5   /||                                                          |     |      |   |    \   5   /||                                                          |    |
   |       |      |sin|-------------||                                                          |     |      |cos|-------------||                                                          |    |
   \       \      \   \      2      //                                                          /     \      \   \      2      //                                                          /    /
$$x < - i \left(\log{\left(\sqrt{\sin^{2}{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)} + \cos^{2}{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)}} \right)} + i \operatorname{atan}{\left(\frac{\cos{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)}}{\sin{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)}} \right)}\right) \wedge - i \left(\log{\left(\sqrt{\sin^{2}{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)} + \cos^{2}{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)}} \right)} + i \operatorname{atan}{\left(\frac{\sin{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)}}{\cos{\left(\frac{\operatorname{atan}{\left(\frac{2 \sqrt{5}}{5} \right)}}{2} \right)}} \right)}\right) < x$$
(x < -i*(i*atan(cos(atan(2*sqrt(5)/5)/2)/sin(atan(2*sqrt(5)/5)/2)) + log(sqrt(cos(atan(2*sqrt(5)/5)/2)^2 + sin(atan(2*sqrt(5)/5)/2)^2))))∧(-i*(i*atan(sin(atan(2*sqrt(5)/5)/2)/cos(atan(2*sqrt(5)/5)/2)) + log(sqrt(cos(atan(2*sqrt(5)/5)/2)^2 + sin(atan(2*sqrt(5)/5)/2)^2))) < x)