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2*cos(x)^2*x+3*cos(x)*x-2<0 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
     2                          
2*cos (x)*x + 3*cos(x)*x - 2 < 0
$$\left(x 3 \cos{\left(x \right)} + x 2 \cos^{2}{\left(x \right)}\right) - 2 < 0$$
x*(3*cos(x)) + x*(2*cos(x)^2) - 2 < 0
Solución detallada
Se da la desigualdad:
$$\left(x 3 \cos{\left(x \right)} + x 2 \cos^{2}{\left(x \right)}\right) - 2 < 0$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$\left(x 3 \cos{\left(x \right)} + x 2 \cos^{2}{\left(x \right)}\right) - 2 = 0$$
Resolvemos:
$$x_{1} = 73.8364027462792$$
$$x_{2} = 61.2718596272267$$
$$x_{3} = 64.3923665126583$$
$$x_{4} = -73.8183410155392$$
$$x_{5} = -54.9656426538452$$
$$x_{6} = -7.94333705294662$$
$$x_{7} = 4.83972949870642$$
$$x_{8} = -39.2870745597143$$
$$x_{9} = -92.6697543756021$$
$$x_{10} = -33.0072014491741$$
$$x_{11} = 1.08247762879257$$
$$x_{12} = 29.8671304442391$$
$$x_{13} = 32.9667646686781$$
$$x_{14} = 83.2442389811335$$
$$x_{15} = -20.4536931796381$$
$$x_{16} = 42.4270534518348$$
$$x_{17} = 51.8235227390457$$
$$x_{18} = 11.0536711207503$$
$$x_{19} = 7.77253236164003$$
$$x_{20} = -58.1310217435679$$
$$x_{21} = 80.118888074651$$
$$x_{22} = -86.3860404813383$$
$$x_{23} = 54.9898987339094$$
$$x_{24} = 58.1080774050884$$
$$x_{25} = -2.06189512827871$$
$$x_{26} = 92.6841420653101$$
$$x_{27} = -76.9777312253131$$
$$x_{28} = -17.2390251987658$$
$$x_{29} = -98.9534008238778$$
$$x_{30} = 14.0912449977744$$
$$x_{31} = 26.6789495533166$$
$$x_{32} = -10.931843121774$$
$$x_{33} = -36.1096191160295$$
$$x_{34} = -14.185754131777$$
$$x_{35} = -64.413071869325$$
$$x_{36} = 67.5540467645286$$
$$x_{37} = 39.2531116528389$$
$$x_{38} = 70.6764604956629$$
$$x_{39} = -61.250092041306$$
$$x_{40} = 89.5279807019346$$
$$x_{41} = -45.5678697547081$$
$$x_{42} = 23.5896961026034$$
$$x_{43} = -48.6808636902234$$
$$x_{44} = 36.1465386061925$$
$$x_{45} = 0.468499276211058$$
$$x_{46} = 86.4014746797018$$
$$x_{47} = -42.3956068566195$$
$$x_{48} = -89.5428732459059$$
$$x_{49} = -95.8255656472355$$
$$x_{50} = 17.3163272961097$$
$$x_{51} = 76.9604068995183$$
$$x_{52} = 20.388331647698$$
$$x_{53} = -26.728911181592$$
$$x_{54} = 45.5385935276166$$
$$x_{55} = -70.6953250285163$$
$$x_{56} = 98.9668749162376$$
$$x_{57} = -80.1022431743895$$
$$x_{58} = -51.8492490822935$$
$$x_{59} = -83.2602556327887$$
$$x_{60} = 48.708250821989$$
$$x_{61} = 95.811649763727$$
$$x_{62} = -23.5330557017427$$
$$x_{63} = -4.54693110505134$$
$$x_{64} = -67.5343045281809$$
$$x_{65} = -29.8224302548231$$
$$x_{1} = 73.8364027462792$$
$$x_{2} = 61.2718596272267$$
$$x_{3} = 64.3923665126583$$
$$x_{4} = -73.8183410155392$$
$$x_{5} = -54.9656426538452$$
$$x_{6} = -7.94333705294662$$
$$x_{7} = 4.83972949870642$$
$$x_{8} = -39.2870745597143$$
$$x_{9} = -92.6697543756021$$
$$x_{10} = -33.0072014491741$$
$$x_{11} = 1.08247762879257$$
$$x_{12} = 29.8671304442391$$
$$x_{13} = 32.9667646686781$$
$$x_{14} = 83.2442389811335$$
$$x_{15} = -20.4536931796381$$
$$x_{16} = 42.4270534518348$$
$$x_{17} = 51.8235227390457$$
$$x_{18} = 11.0536711207503$$
$$x_{19} = 7.77253236164003$$
$$x_{20} = -58.1310217435679$$
$$x_{21} = 80.118888074651$$
$$x_{22} = -86.3860404813383$$
$$x_{23} = 54.9898987339094$$
$$x_{24} = 58.1080774050884$$
$$x_{25} = -2.06189512827871$$
$$x_{26} = 92.6841420653101$$
$$x_{27} = -76.9777312253131$$
$$x_{28} = -17.2390251987658$$
$$x_{29} = -98.9534008238778$$
$$x_{30} = 14.0912449977744$$
$$x_{31} = 26.6789495533166$$
$$x_{32} = -10.931843121774$$
$$x_{33} = -36.1096191160295$$
$$x_{34} = -14.185754131777$$
$$x_{35} = -64.413071869325$$
$$x_{36} = 67.5540467645286$$
$$x_{37} = 39.2531116528389$$
$$x_{38} = 70.6764604956629$$
$$x_{39} = -61.250092041306$$
$$x_{40} = 89.5279807019346$$
$$x_{41} = -45.5678697547081$$
$$x_{42} = 23.5896961026034$$
$$x_{43} = -48.6808636902234$$
$$x_{44} = 36.1465386061925$$
$$x_{45} = 0.468499276211058$$
$$x_{46} = 86.4014746797018$$
$$x_{47} = -42.3956068566195$$
$$x_{48} = -89.5428732459059$$
$$x_{49} = -95.8255656472355$$
$$x_{50} = 17.3163272961097$$
$$x_{51} = 76.9604068995183$$
$$x_{52} = 20.388331647698$$
$$x_{53} = -26.728911181592$$
$$x_{54} = 45.5385935276166$$
$$x_{55} = -70.6953250285163$$
$$x_{56} = 98.9668749162376$$
$$x_{57} = -80.1022431743895$$
$$x_{58} = -51.8492490822935$$
$$x_{59} = -83.2602556327887$$
$$x_{60} = 48.708250821989$$
$$x_{61} = 95.811649763727$$
$$x_{62} = -23.5330557017427$$
$$x_{63} = -4.54693110505134$$
$$x_{64} = -67.5343045281809$$
$$x_{65} = -29.8224302548231$$
Las raíces dadas
$$x_{29} = -98.9534008238778$$
$$x_{49} = -95.8255656472355$$
$$x_{9} = -92.6697543756021$$
$$x_{48} = -89.5428732459059$$
$$x_{22} = -86.3860404813383$$
$$x_{59} = -83.2602556327887$$
$$x_{57} = -80.1022431743895$$
$$x_{27} = -76.9777312253131$$
$$x_{4} = -73.8183410155392$$
$$x_{55} = -70.6953250285163$$
$$x_{64} = -67.5343045281809$$
$$x_{35} = -64.413071869325$$
$$x_{39} = -61.250092041306$$
$$x_{20} = -58.1310217435679$$
$$x_{5} = -54.9656426538452$$
$$x_{58} = -51.8492490822935$$
$$x_{43} = -48.6808636902234$$
$$x_{41} = -45.5678697547081$$
$$x_{47} = -42.3956068566195$$
$$x_{8} = -39.2870745597143$$
$$x_{33} = -36.1096191160295$$
$$x_{10} = -33.0072014491741$$
$$x_{65} = -29.8224302548231$$
$$x_{53} = -26.728911181592$$
$$x_{62} = -23.5330557017427$$
$$x_{15} = -20.4536931796381$$
$$x_{28} = -17.2390251987658$$
$$x_{34} = -14.185754131777$$
$$x_{32} = -10.931843121774$$
$$x_{6} = -7.94333705294662$$
$$x_{63} = -4.54693110505134$$
$$x_{25} = -2.06189512827871$$
$$x_{45} = 0.468499276211058$$
$$x_{11} = 1.08247762879257$$
$$x_{7} = 4.83972949870642$$
$$x_{19} = 7.77253236164003$$
$$x_{18} = 11.0536711207503$$
$$x_{30} = 14.0912449977744$$
$$x_{50} = 17.3163272961097$$
$$x_{52} = 20.388331647698$$
$$x_{42} = 23.5896961026034$$
$$x_{31} = 26.6789495533166$$
$$x_{12} = 29.8671304442391$$
$$x_{13} = 32.9667646686781$$
$$x_{44} = 36.1465386061925$$
$$x_{37} = 39.2531116528389$$
$$x_{16} = 42.4270534518348$$
$$x_{54} = 45.5385935276166$$
$$x_{60} = 48.708250821989$$
$$x_{17} = 51.8235227390457$$
$$x_{23} = 54.9898987339094$$
$$x_{24} = 58.1080774050884$$
$$x_{2} = 61.2718596272267$$
$$x_{3} = 64.3923665126583$$
$$x_{36} = 67.5540467645286$$
$$x_{38} = 70.6764604956629$$
$$x_{1} = 73.8364027462792$$
$$x_{51} = 76.9604068995183$$
$$x_{21} = 80.118888074651$$
$$x_{14} = 83.2442389811335$$
$$x_{46} = 86.4014746797018$$
$$x_{40} = 89.5279807019346$$
$$x_{26} = 92.6841420653101$$
$$x_{61} = 95.811649763727$$
$$x_{56} = 98.9668749162376$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} < x_{29}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{29} - \frac{1}{10}$$
=
$$-98.9534008238778 + - \frac{1}{10}$$
=
$$-99.0534008238778$$
lo sustituimos en la expresión
$$\left(x 3 \cos{\left(x \right)} + x 2 \cos^{2}{\left(x \right)}\right) - 2 < 0$$
$$\left(\left(-99.0534008238778\right) 3 \cos{\left(-99.0534008238778 \right)} + \left(-99.0534008238778\right) 2 \cos^{2}{\left(-99.0534008238778 \right)}\right) - 2 < 0$$
-31.3818014249216 < 0

significa que una de las soluciones de nuestra ecuación será con:
$$x < -98.9534008238778$$
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-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------ο-------
       x29      x49      x9      x48      x22      x59      x57      x27      x4      x55      x64      x35      x39      x20      x5      x58      x43      x41      x47      x8      x33      x10      x65      x53      x62      x15      x28      x34      x32      x6      x63      x25      x45      x11      x7      x19      x18      x30      x50      x52      x42      x31      x12      x13      x44      x37      x16      x54      x60      x17      x23      x24      x2      x3      x36      x38      x1      x51      x21      x14      x46      x40      x26      x61      x56

Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x < -98.9534008238778$$
$$x > -95.8255656472355 \wedge x < -92.6697543756021$$
$$x > -89.5428732459059 \wedge x < -86.3860404813383$$
$$x > -83.2602556327887 \wedge x < -80.1022431743895$$
$$x > -76.9777312253131 \wedge x < -73.8183410155392$$
$$x > -70.6953250285163 \wedge x < -67.5343045281809$$
$$x > -64.413071869325 \wedge x < -61.250092041306$$
$$x > -58.1310217435679 \wedge x < -54.9656426538452$$
$$x > -51.8492490822935 \wedge x < -48.6808636902234$$
$$x > -45.5678697547081 \wedge x < -42.3956068566195$$
$$x > -39.2870745597143 \wedge x < -36.1096191160295$$
$$x > -33.0072014491741 \wedge x < -29.8224302548231$$
$$x > -26.728911181592 \wedge x < -23.5330557017427$$
$$x > -20.4536931796381 \wedge x < -17.2390251987658$$
$$x > -14.185754131777 \wedge x < -10.931843121774$$
$$x > -7.94333705294662 \wedge x < -4.54693110505134$$
$$x > -2.06189512827871 \wedge x < 0.468499276211058$$
$$x > 1.08247762879257 \wedge x < 4.83972949870642$$
$$x > 7.77253236164003 \wedge x < 11.0536711207503$$
$$x > 14.0912449977744 \wedge x < 17.3163272961097$$
$$x > 20.388331647698 \wedge x < 23.5896961026034$$
$$x > 26.6789495533166 \wedge x < 29.8671304442391$$
$$x > 32.9667646686781 \wedge x < 36.1465386061925$$
$$x > 39.2531116528389 \wedge x < 42.4270534518348$$
$$x > 45.5385935276166 \wedge x < 48.708250821989$$
$$x > 51.8235227390457 \wedge x < 54.9898987339094$$
$$x > 58.1080774050884 \wedge x < 61.2718596272267$$
$$x > 64.3923665126583 \wedge x < 67.5540467645286$$
$$x > 70.6764604956629 \wedge x < 73.8364027462792$$
$$x > 76.9604068995183 \wedge x < 80.118888074651$$
$$x > 83.2442389811335 \wedge x < 86.4014746797018$$
$$x > 89.5279807019346 \wedge x < 92.6841420653101$$
$$x > 95.811649763727 \wedge x < 98.9668749162376$$
Solución de la desigualdad en el gráfico