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(ctg(2*x))^2-3ctg(x)+2>=0 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
   2                         
cot (2*x) - 3*cot(x) + 2 >= 0
$$\left(- 3 \cot{\left(x \right)} + \cot^{2}{\left(2 x \right)}\right) + 2 \geq 0$$
-3*cot(x) + cot(2*x)^2 + 2 >= 0
Solución detallada
Se da la desigualdad:
$$\left(- 3 \cot{\left(x \right)} + \cot^{2}{\left(2 x \right)}\right) + 2 \geq 0$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$\left(- 3 \cot{\left(x \right)} + \cot^{2}{\left(2 x \right)}\right) + 2 = 0$$
Resolvemos:
Tenemos la ecuación
$$\left(- 3 \cot{\left(x \right)} + \cot^{2}{\left(2 x \right)}\right) + 2 = 0$$
cambiamos
$$- 3 \cot{\left(x \right)} + \cot^{2}{\left(2 x \right)} + 1 = 0$$
$$- 3 \cot{\left(x \right)} + \cot^{2}{\left(2 x \right)} + 1 = 0$$
Sustituimos
$$w = \cot{\left(2 x \right)}$$
Es la ecuación de la forma
a*w^2 + b*w + c = 0

La ecuación cuadrática puede ser resuelta
con la ayuda del discriminante.
Las raíces de la ecuación cuadrática:
$$w_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$w_{2} = \frac{- \sqrt{D} - b}{2 a}$$
donde D = b^2 - 4*a*c es el discriminante.
Como
$$a = 1$$
$$b = 0$$
$$c = 1 - 3 \cot{\left(x \right)}$$
, entonces
D = b^2 - 4 * a * c = 

(0)^2 - 4 * (1) * (1 - 3*cot(x)) = -4 + 12*cot(x)

La ecuación tiene dos raíces.
w1 = (-b + sqrt(D)) / (2*a)

w2 = (-b - sqrt(D)) / (2*a)

o
$$w_{1} = \frac{\sqrt{12 \cot{\left(x \right)} - 4}}{2}$$
$$w_{2} = - \frac{\sqrt{12 \cot{\left(x \right)} - 4}}{2}$$
hacemos cambio inverso
$$\cot{\left(2 x \right)} = w$$
sustituimos w:
$$x_{1} = -2.1868803298028$$
$$x_{2} = 7.23789763096658$$
$$x_{3} = 66.9281580491727$$
$$x_{4} = 82.6361213171216$$
$$x_{5} = -14.753250944162$$
$$x_{6} = 79.4945286635318$$
$$x_{7} = -27.3196215585211$$
$$x_{8} = -99.5762525910864$$
$$x_{9} = 98.3440845850706$$
$$x_{10} = 76.352936009942$$
$$x_{11} = 13.5210829381462$$
$$x_{12} = 0.954712323786992$$
$$x_{13} = 54.3617874348135$$
$$x_{14} = 22.9458608989155$$
$$x_{15} = -93.2930672839068$$
$$x_{16} = 2646.17572664639$$
$$x_{17} = -77.5851040159578$$
$$x_{18} = -65.0187334015987$$
$$x_{19} = 48.0786021276339$$
$$x_{20} = 70.0697507027624$$
$$x_{21} = -83.8682893231374$$
$$x_{22} = -71.3019187087783$$
$$x_{23} = -87.0098819767272$$
$$x_{24} = -33.6028068657007$$
$$x_{25} = -61.8771407480089$$
$$x_{26} = 95.2024919314808$$
$$x_{27} = -43.0275848264701$$
$$x_{28} = 10.3794902845564$$
$$x_{29} = -30.4612142121109$$
$$x_{30} = 26.0874535525053$$
$$x_{31} = -39.8859921728803$$
$$x_{32} = 41.7954168204543$$
$$x_{33} = 19.8042682453258$$
$$x_{34} = 60.6449727419931$$
$$x_{35} = 62.9187678846351$$
$$x_{36} = -68.1603260551885$$
$$x_{37} = 16.662675591736$$
$$x_{38} = -52.4523627872395$$
$$x_{39} = 38.6538241668645$$
$$x_{40} = 32.3706388596849$$
$$x_{41} = -24.1780289049314$$
$$x_{42} = -49.3107701336497$$
$$x_{43} = -5.32847298339259$$
$$x_{44} = -21.0364362513416$$
$$x_{45} = -96.4346599374966$$
$$x_{46} = 44.9370094740441$$
$$x_{47} = -36.7443995192905$$
$$x_{48} = -8.47006563698239$$
$$x_{49} = -90.151474630317$$
$$x_{50} = 63.7865653955829$$
$$x_{51} = 92.060899277891$$
$$x_{52} = -17.8948435977518$$
$$x_{53} = -74.443511362368$$
$$x_{54} = 88.9193066243012$$
$$x_{55} = -46.1691774800599$$
$$x_{56} = 4.09630497737678$$
$$x_{57} = -11.6116582905722$$
$$x_{58} = 85.7777139707114$$
$$x_{59} = -55.5939554408293$$
$$x_{1} = -2.1868803298028$$
$$x_{2} = 7.23789763096658$$
$$x_{3} = 66.9281580491727$$
$$x_{4} = 82.6361213171216$$
$$x_{5} = -14.753250944162$$
$$x_{6} = 79.4945286635318$$
$$x_{7} = -27.3196215585211$$
$$x_{8} = -99.5762525910864$$
$$x_{9} = 98.3440845850706$$
$$x_{10} = 76.352936009942$$
$$x_{11} = 13.5210829381462$$
$$x_{12} = 0.954712323786992$$
$$x_{13} = 54.3617874348135$$
$$x_{14} = 22.9458608989155$$
$$x_{15} = -93.2930672839068$$
$$x_{16} = 2646.17572664639$$
$$x_{17} = -77.5851040159578$$
$$x_{18} = -65.0187334015987$$
$$x_{19} = 48.0786021276339$$
$$x_{20} = 70.0697507027624$$
$$x_{21} = -83.8682893231374$$
$$x_{22} = -71.3019187087783$$
$$x_{23} = -87.0098819767272$$
$$x_{24} = -33.6028068657007$$
$$x_{25} = -61.8771407480089$$
$$x_{26} = 95.2024919314808$$
$$x_{27} = -43.0275848264701$$
$$x_{28} = 10.3794902845564$$
$$x_{29} = -30.4612142121109$$
$$x_{30} = 26.0874535525053$$
$$x_{31} = -39.8859921728803$$
$$x_{32} = 41.7954168204543$$
$$x_{33} = 19.8042682453258$$
$$x_{34} = 60.6449727419931$$
$$x_{35} = 62.9187678846351$$
$$x_{36} = -68.1603260551885$$
$$x_{37} = 16.662675591736$$
$$x_{38} = -52.4523627872395$$
$$x_{39} = 38.6538241668645$$
$$x_{40} = 32.3706388596849$$
$$x_{41} = -24.1780289049314$$
$$x_{42} = -49.3107701336497$$
$$x_{43} = -5.32847298339259$$
$$x_{44} = -21.0364362513416$$
$$x_{45} = -96.4346599374966$$
$$x_{46} = 44.9370094740441$$
$$x_{47} = -36.7443995192905$$
$$x_{48} = -8.47006563698239$$
$$x_{49} = -90.151474630317$$
$$x_{50} = 63.7865653955829$$
$$x_{51} = 92.060899277891$$
$$x_{52} = -17.8948435977518$$
$$x_{53} = -74.443511362368$$
$$x_{54} = 88.9193066243012$$
$$x_{55} = -46.1691774800599$$
$$x_{56} = 4.09630497737678$$
$$x_{57} = -11.6116582905722$$
$$x_{58} = 85.7777139707114$$
$$x_{59} = -55.5939554408293$$
Las raíces dadas
$$x_{8} = -99.5762525910864$$
$$x_{45} = -96.4346599374966$$
$$x_{15} = -93.2930672839068$$
$$x_{49} = -90.151474630317$$
$$x_{23} = -87.0098819767272$$
$$x_{21} = -83.8682893231374$$
$$x_{17} = -77.5851040159578$$
$$x_{53} = -74.443511362368$$
$$x_{22} = -71.3019187087783$$
$$x_{36} = -68.1603260551885$$
$$x_{18} = -65.0187334015987$$
$$x_{25} = -61.8771407480089$$
$$x_{59} = -55.5939554408293$$
$$x_{38} = -52.4523627872395$$
$$x_{42} = -49.3107701336497$$
$$x_{55} = -46.1691774800599$$
$$x_{27} = -43.0275848264701$$
$$x_{31} = -39.8859921728803$$
$$x_{47} = -36.7443995192905$$
$$x_{24} = -33.6028068657007$$
$$x_{29} = -30.4612142121109$$
$$x_{7} = -27.3196215585211$$
$$x_{41} = -24.1780289049314$$
$$x_{44} = -21.0364362513416$$
$$x_{52} = -17.8948435977518$$
$$x_{5} = -14.753250944162$$
$$x_{57} = -11.6116582905722$$
$$x_{48} = -8.47006563698239$$
$$x_{43} = -5.32847298339259$$
$$x_{1} = -2.1868803298028$$
$$x_{12} = 0.954712323786992$$
$$x_{56} = 4.09630497737678$$
$$x_{2} = 7.23789763096658$$
$$x_{28} = 10.3794902845564$$
$$x_{11} = 13.5210829381462$$
$$x_{37} = 16.662675591736$$
$$x_{33} = 19.8042682453258$$
$$x_{14} = 22.9458608989155$$
$$x_{30} = 26.0874535525053$$
$$x_{40} = 32.3706388596849$$
$$x_{39} = 38.6538241668645$$
$$x_{32} = 41.7954168204543$$
$$x_{46} = 44.9370094740441$$
$$x_{19} = 48.0786021276339$$
$$x_{13} = 54.3617874348135$$
$$x_{34} = 60.6449727419931$$
$$x_{35} = 62.9187678846351$$
$$x_{50} = 63.7865653955829$$
$$x_{3} = 66.9281580491727$$
$$x_{20} = 70.0697507027624$$
$$x_{10} = 76.352936009942$$
$$x_{6} = 79.4945286635318$$
$$x_{4} = 82.6361213171216$$
$$x_{58} = 85.7777139707114$$
$$x_{54} = 88.9193066243012$$
$$x_{51} = 92.060899277891$$
$$x_{26} = 95.2024919314808$$
$$x_{9} = 98.3440845850706$$
$$x_{16} = 2646.17572664639$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} \leq x_{8}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{8} - \frac{1}{10}$$
=
$$-99.5762525910864 + - \frac{1}{10}$$
=
$$-99.6762525910864$$
lo sustituimos en la expresión
$$\left(- 3 \cot{\left(x \right)} + \cot^{2}{\left(2 x \right)}\right) + 2 \geq 0$$
$$\left(- 3 \cot{\left(-99.6762525910864 \right)} + \cot^{2}{\left(\left(-99.6762525910864\right) 2 \right)}\right) + 2 \geq 0$$
-0.591022891543910 >= 0

pero
-0.591022891543910 < 0

Entonces
$$x \leq -99.5762525910864$$
no se cumple
significa que una de las soluciones de nuestra ecuación será con:
$$x \geq -99.5762525910864 \wedge x \leq -96.4346599374966$$
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       x8      x45      x15      x49      x23      x21      x17      x53      x22      x36      x18      x25      x59      x38      x42      x55      x27      x31      x47      x24      x29      x7      x41      x44      x52      x5      x57      x48      x43      x1      x12      x56      x2      x28      x11      x37      x33      x14      x30      x40      x39      x32      x46      x19      x13      x34      x35      x50      x3      x20      x10      x6      x4      x58      x54      x51      x26      x9      x16

Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x \geq -99.5762525910864 \wedge x \leq -96.4346599374966$$
$$x \geq -93.2930672839068 \wedge x \leq -90.151474630317$$
$$x \geq -87.0098819767272 \wedge x \leq -83.8682893231374$$
$$x \geq -77.5851040159578 \wedge x \leq -74.443511362368$$
$$x \geq -71.3019187087783 \wedge x \leq -68.1603260551885$$
$$x \geq -65.0187334015987 \wedge x \leq -61.8771407480089$$
$$x \geq -55.5939554408293 \wedge x \leq -52.4523627872395$$
$$x \geq -49.3107701336497 \wedge x \leq -46.1691774800599$$
$$x \geq -43.0275848264701 \wedge x \leq -39.8859921728803$$
$$x \geq -36.7443995192905 \wedge x \leq -33.6028068657007$$
$$x \geq -30.4612142121109 \wedge x \leq -27.3196215585211$$
$$x \geq -24.1780289049314 \wedge x \leq -21.0364362513416$$
$$x \geq -17.8948435977518 \wedge x \leq -14.753250944162$$
$$x \geq -11.6116582905722 \wedge x \leq -8.47006563698239$$
$$x \geq -5.32847298339259 \wedge x \leq -2.1868803298028$$
$$x \geq 0.954712323786992 \wedge x \leq 4.09630497737678$$
$$x \geq 7.23789763096658 \wedge x \leq 10.3794902845564$$
$$x \geq 13.5210829381462 \wedge x \leq 16.662675591736$$
$$x \geq 19.8042682453258 \wedge x \leq 22.9458608989155$$
$$x \geq 26.0874535525053 \wedge x \leq 32.3706388596849$$
$$x \geq 38.6538241668645 \wedge x \leq 41.7954168204543$$
$$x \geq 44.9370094740441 \wedge x \leq 48.0786021276339$$
$$x \geq 54.3617874348135 \wedge x \leq 60.6449727419931$$
$$x \geq 62.9187678846351 \wedge x \leq 63.7865653955829$$
$$x \geq 66.9281580491727 \wedge x \leq 70.0697507027624$$
$$x \geq 76.352936009942 \wedge x \leq 79.4945286635318$$
$$x \geq 82.6361213171216 \wedge x \leq 85.7777139707114$$
$$x \geq 88.9193066243012 \wedge x \leq 92.060899277891$$
$$x \geq 95.2024919314808 \wedge x \leq 98.3440845850706$$
$$x \geq 2646.17572664639$$