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sin(x/2)xcos(x/2)>1/2 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
   /x\      /x\      
sin|-|*x*cos|-| > 1/2
   \2/      \2/      
$$x \sin{\left(\frac{x}{2} \right)} \cos{\left(\frac{x}{2} \right)} > \frac{1}{2}$$
(x*sin(x/2))*cos(x/2) > 1/2
Solución detallada
Se da la desigualdad:
$$x \sin{\left(\frac{x}{2} \right)} \cos{\left(\frac{x}{2} \right)} > \frac{1}{2}$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$x \sin{\left(\frac{x}{2} \right)} \cos{\left(\frac{x}{2} \right)} = \frac{1}{2}$$
Resolvemos:
$$x_{1} = 18.9024837303424$$
$$x_{2} = 65.9582840466332$$
$$x_{3} = 21.9455654988197$$
$$x_{4} = 100.540911278755$$
$$x_{5} = -94.2583889420049$$
$$x_{6} = -81.6936501525055$$
$$x_{7} = 53.3883433351401$$
$$x_{8} = -69.12950448699$$
$$x_{9} = -97.3791029371005$$
$$x_{10} = 47.1026579842757$$
$$x_{11} = 69.12950448699$$
$$x_{12} = -2.77260470826599$$
$$x_{13} = 37.7256221319914$$
$$x_{14} = 15.6439973747731$$
$$x_{15} = -84.811210479617$$
$$x_{16} = -75.4114846544819$$
$$x_{17} = 87.9759612866821$$
$$x_{18} = -53.3883433351401$$
$$x_{19} = 59.6735017769259$$
$$x_{20} = 9.31724294141481$$
$$x_{21} = -62.8477652080076$$
$$x_{22} = -25.1724776117344$$
$$x_{23} = 50.2853702681169$$
$$x_{24} = -56.5663470412005$$
$$x_{25} = 1.11415714087193$$
$$x_{26} = -12.6455325787891$$
$$x_{27} = -40.8162019701941$$
$$x_{28} = -100.540911278755$$
$$x_{29} = -50.2853702681169$$
$$x_{30} = 81.6936501525055$$
$$x_{31} = -87.9759612866821$$
$$x_{32} = -103.662910767087$$
$$x_{33} = -18.9024837303424$$
$$x_{34} = 25.1724776117344$$
$$x_{35} = -44.0050237846841$$
$$x_{36} = 84.811210479617$$
$$x_{37} = -78.5270815352651$$
$$x_{38} = -72.2427883783755$$
$$x_{39} = 34.5285536017763$$
$$x_{40} = 56.5663470412005$$
$$x_{41} = 62.8477652080076$$
$$x_{42} = 12.6455325787891$$
$$x_{43} = 75.4114846544819$$
$$x_{44} = -15.6439973747731$$
$$x_{45} = -47.1026579842757$$
$$x_{46} = 31.4477306941599$$
$$x_{47} = -21.9455654988197$$
$$x_{48} = -59.6735017769259$$
$$x_{49} = -65.9582840466332$$
$$x_{50} = 97.3791029371005$$
$$x_{51} = 94.2583889420049$$
$$x_{52} = 28.238914350639$$
$$x_{53} = 44.0050237846841$$
$$x_{54} = -31.4477306941599$$
$$x_{55} = -9.31724294141481$$
$$x_{56} = -91.0952092079181$$
$$x_{57} = 78.5270815352651$$
$$x_{58} = 72.2427883783755$$
$$x_{59} = 91.0952092079181$$
$$x_{60} = -34.5285536017763$$
$$x_{61} = 2.77260470826599$$
$$x_{62} = -1.11415714087193$$
$$x_{63} = -37.7256221319914$$
$$x_{64} = -6.43911723841725$$
$$x_{65} = -28.238914350639$$
$$x_{66} = 40.8162019701941$$
$$x_{67} = 6.43911723841725$$
$$x_{1} = 18.9024837303424$$
$$x_{2} = 65.9582840466332$$
$$x_{3} = 21.9455654988197$$
$$x_{4} = 100.540911278755$$
$$x_{5} = -94.2583889420049$$
$$x_{6} = -81.6936501525055$$
$$x_{7} = 53.3883433351401$$
$$x_{8} = -69.12950448699$$
$$x_{9} = -97.3791029371005$$
$$x_{10} = 47.1026579842757$$
$$x_{11} = 69.12950448699$$
$$x_{12} = -2.77260470826599$$
$$x_{13} = 37.7256221319914$$
$$x_{14} = 15.6439973747731$$
$$x_{15} = -84.811210479617$$
$$x_{16} = -75.4114846544819$$
$$x_{17} = 87.9759612866821$$
$$x_{18} = -53.3883433351401$$
$$x_{19} = 59.6735017769259$$
$$x_{20} = 9.31724294141481$$
$$x_{21} = -62.8477652080076$$
$$x_{22} = -25.1724776117344$$
$$x_{23} = 50.2853702681169$$
$$x_{24} = -56.5663470412005$$
$$x_{25} = 1.11415714087193$$
$$x_{26} = -12.6455325787891$$
$$x_{27} = -40.8162019701941$$
$$x_{28} = -100.540911278755$$
$$x_{29} = -50.2853702681169$$
$$x_{30} = 81.6936501525055$$
$$x_{31} = -87.9759612866821$$
$$x_{32} = -103.662910767087$$
$$x_{33} = -18.9024837303424$$
$$x_{34} = 25.1724776117344$$
$$x_{35} = -44.0050237846841$$
$$x_{36} = 84.811210479617$$
$$x_{37} = -78.5270815352651$$
$$x_{38} = -72.2427883783755$$
$$x_{39} = 34.5285536017763$$
$$x_{40} = 56.5663470412005$$
$$x_{41} = 62.8477652080076$$
$$x_{42} = 12.6455325787891$$
$$x_{43} = 75.4114846544819$$
$$x_{44} = -15.6439973747731$$
$$x_{45} = -47.1026579842757$$
$$x_{46} = 31.4477306941599$$
$$x_{47} = -21.9455654988197$$
$$x_{48} = -59.6735017769259$$
$$x_{49} = -65.9582840466332$$
$$x_{50} = 97.3791029371005$$
$$x_{51} = 94.2583889420049$$
$$x_{52} = 28.238914350639$$
$$x_{53} = 44.0050237846841$$
$$x_{54} = -31.4477306941599$$
$$x_{55} = -9.31724294141481$$
$$x_{56} = -91.0952092079181$$
$$x_{57} = 78.5270815352651$$
$$x_{58} = 72.2427883783755$$
$$x_{59} = 91.0952092079181$$
$$x_{60} = -34.5285536017763$$
$$x_{61} = 2.77260470826599$$
$$x_{62} = -1.11415714087193$$
$$x_{63} = -37.7256221319914$$
$$x_{64} = -6.43911723841725$$
$$x_{65} = -28.238914350639$$
$$x_{66} = 40.8162019701941$$
$$x_{67} = 6.43911723841725$$
Las raíces dadas
$$x_{32} = -103.662910767087$$
$$x_{28} = -100.540911278755$$
$$x_{9} = -97.3791029371005$$
$$x_{5} = -94.2583889420049$$
$$x_{56} = -91.0952092079181$$
$$x_{31} = -87.9759612866821$$
$$x_{15} = -84.811210479617$$
$$x_{6} = -81.6936501525055$$
$$x_{37} = -78.5270815352651$$
$$x_{16} = -75.4114846544819$$
$$x_{38} = -72.2427883783755$$
$$x_{8} = -69.12950448699$$
$$x_{49} = -65.9582840466332$$
$$x_{21} = -62.8477652080076$$
$$x_{48} = -59.6735017769259$$
$$x_{24} = -56.5663470412005$$
$$x_{18} = -53.3883433351401$$
$$x_{29} = -50.2853702681169$$
$$x_{45} = -47.1026579842757$$
$$x_{35} = -44.0050237846841$$
$$x_{27} = -40.8162019701941$$
$$x_{63} = -37.7256221319914$$
$$x_{60} = -34.5285536017763$$
$$x_{54} = -31.4477306941599$$
$$x_{65} = -28.238914350639$$
$$x_{22} = -25.1724776117344$$
$$x_{47} = -21.9455654988197$$
$$x_{33} = -18.9024837303424$$
$$x_{44} = -15.6439973747731$$
$$x_{26} = -12.6455325787891$$
$$x_{55} = -9.31724294141481$$
$$x_{64} = -6.43911723841725$$
$$x_{12} = -2.77260470826599$$
$$x_{62} = -1.11415714087193$$
$$x_{25} = 1.11415714087193$$
$$x_{61} = 2.77260470826599$$
$$x_{67} = 6.43911723841725$$
$$x_{20} = 9.31724294141481$$
$$x_{42} = 12.6455325787891$$
$$x_{14} = 15.6439973747731$$
$$x_{1} = 18.9024837303424$$
$$x_{3} = 21.9455654988197$$
$$x_{34} = 25.1724776117344$$
$$x_{52} = 28.238914350639$$
$$x_{46} = 31.4477306941599$$
$$x_{39} = 34.5285536017763$$
$$x_{13} = 37.7256221319914$$
$$x_{66} = 40.8162019701941$$
$$x_{53} = 44.0050237846841$$
$$x_{10} = 47.1026579842757$$
$$x_{23} = 50.2853702681169$$
$$x_{7} = 53.3883433351401$$
$$x_{40} = 56.5663470412005$$
$$x_{19} = 59.6735017769259$$
$$x_{41} = 62.8477652080076$$
$$x_{2} = 65.9582840466332$$
$$x_{11} = 69.12950448699$$
$$x_{58} = 72.2427883783755$$
$$x_{43} = 75.4114846544819$$
$$x_{57} = 78.5270815352651$$
$$x_{30} = 81.6936501525055$$
$$x_{36} = 84.811210479617$$
$$x_{17} = 87.9759612866821$$
$$x_{59} = 91.0952092079181$$
$$x_{51} = 94.2583889420049$$
$$x_{50} = 97.3791029371005$$
$$x_{4} = 100.540911278755$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} < x_{32}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{32} - \frac{1}{10}$$
=
$$-103.662910767087 + - \frac{1}{10}$$
=
$$-103.762910767086$$
lo sustituimos en la expresión
$$x \sin{\left(\frac{x}{2} \right)} \cos{\left(\frac{x}{2} \right)} > \frac{1}{2}$$
$$\left(-103.762910767086\right) \sin{\left(- \frac{103.762910767086}{2} \right)} \cos{\left(- \frac{103.762910767086}{2} \right)} > \frac{1}{2}$$
-4.68127994356077 > 1/2

Entonces
$$x < -103.662910767087$$
no se cumple
significa que una de las soluciones de nuestra ecuación será con:
$$x > -103.662910767087 \wedge x < -100.540911278755$$
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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-------ο-------ο-------
       x32      x28      x9      x5      x56      x31      x15      x6      x37      x16      x38      x8      x49      x21      x48      x24      x18      x29      x45      x35      x27      x63      x60      x54      x65      x22      x47      x33      x44      x26      x55      x64      x12      x62      x25      x61      x67      x20      x42      x14      x1      x3      x34      x52      x46      x39      x13      x66      x53      x10      x23      x7      x40      x19      x41      x2      x11      x58      x43      x57      x30      x36      x17      x59      x51      x50      x4

Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x > -103.662910767087 \wedge x < -100.540911278755$$
$$x > -97.3791029371005 \wedge x < -94.2583889420049$$
$$x > -91.0952092079181 \wedge x < -87.9759612866821$$
$$x > -84.811210479617 \wedge x < -81.6936501525055$$
$$x > -78.5270815352651 \wedge x < -75.4114846544819$$
$$x > -72.2427883783755 \wedge x < -69.12950448699$$
$$x > -65.9582840466332 \wedge x < -62.8477652080076$$
$$x > -59.6735017769259 \wedge x < -56.5663470412005$$
$$x > -53.3883433351401 \wedge x < -50.2853702681169$$
$$x > -47.1026579842757 \wedge x < -44.0050237846841$$
$$x > -40.8162019701941 \wedge x < -37.7256221319914$$
$$x > -34.5285536017763 \wedge x < -31.4477306941599$$
$$x > -28.238914350639 \wedge x < -25.1724776117344$$
$$x > -21.9455654988197 \wedge x < -18.9024837303424$$
$$x > -15.6439973747731 \wedge x < -12.6455325787891$$
$$x > -9.31724294141481 \wedge x < -6.43911723841725$$
$$x > -2.77260470826599 \wedge x < -1.11415714087193$$
$$x > 1.11415714087193 \wedge x < 2.77260470826599$$
$$x > 6.43911723841725 \wedge x < 9.31724294141481$$
$$x > 12.6455325787891 \wedge x < 15.6439973747731$$
$$x > 18.9024837303424 \wedge x < 21.9455654988197$$
$$x > 25.1724776117344 \wedge x < 28.238914350639$$
$$x > 31.4477306941599 \wedge x < 34.5285536017763$$
$$x > 37.7256221319914 \wedge x < 40.8162019701941$$
$$x > 44.0050237846841 \wedge x < 47.1026579842757$$
$$x > 50.2853702681169 \wedge x < 53.3883433351401$$
$$x > 56.5663470412005 \wedge x < 59.6735017769259$$
$$x > 62.8477652080076 \wedge x < 65.9582840466332$$
$$x > 69.12950448699 \wedge x < 72.2427883783755$$
$$x > 75.4114846544819 \wedge x < 78.5270815352651$$
$$x > 81.6936501525055 \wedge x < 84.811210479617$$
$$x > 87.9759612866821 \wedge x < 91.0952092079181$$
$$x > 94.2583889420049 \wedge x < 97.3791029371005$$
$$x > 100.540911278755$$
Solución de la desigualdad en el gráfico