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abs(cos(x))<1/2 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
|cos(x)| < 1/2
$$\left|{\cos{\left(x \right)}}\right| < \frac{1}{2}$$
Abs(cos(x)) < 1/2
Solución detallada
Se da la desigualdad:
$$\left|{\cos{\left(x \right)}}\right| < \frac{1}{2}$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$\left|{\cos{\left(x \right)}}\right| = \frac{1}{2}$$
Resolvemos:
Tenemos la ecuación
$$\left|{\cos{\left(x \right)}}\right| = \frac{1}{2}$$
cambiamos
$$\left|{\cos{\left(x \right)}}\right| - \frac{1}{2} = 0$$
$$\left|{\cos{\left(x \right)}}\right| - \frac{1}{2} = 0$$
Sustituimos
$$w = \left|{\cos{\left(x \right)}}\right|$$
Transportamos los términos libres (sin w)
del miembro izquierdo al derecho, obtenemos:
$$w = \frac{1}{2}$$
Obtenemos la respuesta: w = 1/2
hacemos cambio inverso
$$\left|{\cos{\left(x \right)}}\right| = w$$
sustituimos w:
$$x_{1} = -93.2005820564972$$
$$x_{2} = -68.0678408277789$$
$$x_{3} = -79.5870138909414$$
$$x_{4} = 63.8790506229925$$
$$x_{5} = 82.7286065445312$$
$$x_{6} = -85.870199198121$$
$$x_{7} = -4.18879020478639$$
$$x_{8} = 74.3510261349584$$
$$x_{9} = 61.7846555205993$$
$$x_{10} = -35.6047167406843$$
$$x_{11} = 2.0943951023932$$
$$x_{12} = 33.5103216382911$$
$$x_{13} = -76.4454212373516$$
$$x_{14} = -32.4631240870945$$
$$x_{15} = 30.3687289847013$$
$$x_{16} = -63.8790506229925$$
$$x_{17} = 39.7935069454707$$
$$x_{18} = -70.162235930172$$
$$x_{19} = 70.162235930172$$
$$x_{20} = 269.129770657526$$
$$x_{21} = 38.7463093942741$$
$$x_{22} = 76.4454212373516$$
$$x_{23} = -39.7935069454707$$
$$x_{24} = -77.4926187885482$$
$$x_{25} = -96.342174710087$$
$$x_{26} = 85.870199198121$$
$$x_{27} = 98.4365698124802$$
$$x_{28} = -24.0855436775217$$
$$x_{29} = -90.0589894029074$$
$$x_{30} = -41.8879020478639$$
$$x_{31} = -673.348025419412$$
$$x_{32} = 60.7374579694027$$
$$x_{33} = 90.0589894029074$$
$$x_{34} = 275.412955964705$$
$$x_{35} = -2.0943951023932$$
$$x_{36} = 41.8879020478639$$
$$x_{37} = -74.3510261349584$$
$$x_{38} = 26.1799387799149$$
$$x_{39} = 55.5014702134197$$
$$x_{40} = -61.7846555205993$$
$$x_{41} = 68.0678408277789$$
$$x_{42} = -13.6135681655558$$
$$x_{43} = -55.5014702134197$$
$$x_{44} = -30.3687289847013$$
$$x_{45} = 77.4926187885482$$
$$x_{46} = -26.1799387799149$$
$$x_{47} = 8.37758040957278$$
$$x_{48} = 52.3598775598299$$
$$x_{49} = -46.0766922526503$$
$$x_{50} = -33.5103216382911$$
$$x_{51} = 16.7551608191456$$
$$x_{52} = -60.7374579694027$$
$$x_{53} = -99.4837673636768$$
$$x_{54} = -27.2271363311115$$
$$x_{55} = -5.23598775598299$$
$$x_{56} = 96.342174710087$$
$$x_{57} = -11.5191730631626$$
$$x_{58} = -83.7758040957278$$
$$x_{59} = -54.4542726622231$$
$$x_{60} = 3803.42150594604$$
$$x_{61} = 19.8967534727354$$
$$x_{62} = 48.1710873550435$$
$$x_{63} = -49.2182849062401$$
$$x_{64} = -10.471975511966$$
$$x_{65} = 4.18879020478639$$
$$x_{66} = 32.4631240870945$$
$$x_{67} = 11.5191730631626$$
$$x_{68} = 83.7758040957278$$
$$x_{69} = -42.9350995990605$$
$$x_{70} = -71.2094334813686$$
$$x_{71} = -19.8967534727354$$
$$x_{72} = 54.4542726622231$$
$$x_{73} = 99.4837673636768$$
$$x_{74} = 92.1533845053006$$
$$x_{75} = -48.1710873550435$$
$$x_{76} = 46.0766922526503$$
$$x_{77} = 24.0855436775217$$
$$x_{78} = 10.471975511966$$
$$x_{79} = 17.8023583703422$$
$$x_{80} = -17.8023583703422$$
$$x_{81} = -57.5958653158129$$
$$x_{82} = -92.1533845053006$$
$$x_{83} = -52.3598775598299$$
$$x_{84} = -98.4365698124802$$
$$x_{1} = -93.2005820564972$$
$$x_{2} = -68.0678408277789$$
$$x_{3} = -79.5870138909414$$
$$x_{4} = 63.8790506229925$$
$$x_{5} = 82.7286065445312$$
$$x_{6} = -85.870199198121$$
$$x_{7} = -4.18879020478639$$
$$x_{8} = 74.3510261349584$$
$$x_{9} = 61.7846555205993$$
$$x_{10} = -35.6047167406843$$
$$x_{11} = 2.0943951023932$$
$$x_{12} = 33.5103216382911$$
$$x_{13} = -76.4454212373516$$
$$x_{14} = -32.4631240870945$$
$$x_{15} = 30.3687289847013$$
$$x_{16} = -63.8790506229925$$
$$x_{17} = 39.7935069454707$$
$$x_{18} = -70.162235930172$$
$$x_{19} = 70.162235930172$$
$$x_{20} = 269.129770657526$$
$$x_{21} = 38.7463093942741$$
$$x_{22} = 76.4454212373516$$
$$x_{23} = -39.7935069454707$$
$$x_{24} = -77.4926187885482$$
$$x_{25} = -96.342174710087$$
$$x_{26} = 85.870199198121$$
$$x_{27} = 98.4365698124802$$
$$x_{28} = -24.0855436775217$$
$$x_{29} = -90.0589894029074$$
$$x_{30} = -41.8879020478639$$
$$x_{31} = -673.348025419412$$
$$x_{32} = 60.7374579694027$$
$$x_{33} = 90.0589894029074$$
$$x_{34} = 275.412955964705$$
$$x_{35} = -2.0943951023932$$
$$x_{36} = 41.8879020478639$$
$$x_{37} = -74.3510261349584$$
$$x_{38} = 26.1799387799149$$
$$x_{39} = 55.5014702134197$$
$$x_{40} = -61.7846555205993$$
$$x_{41} = 68.0678408277789$$
$$x_{42} = -13.6135681655558$$
$$x_{43} = -55.5014702134197$$
$$x_{44} = -30.3687289847013$$
$$x_{45} = 77.4926187885482$$
$$x_{46} = -26.1799387799149$$
$$x_{47} = 8.37758040957278$$
$$x_{48} = 52.3598775598299$$
$$x_{49} = -46.0766922526503$$
$$x_{50} = -33.5103216382911$$
$$x_{51} = 16.7551608191456$$
$$x_{52} = -60.7374579694027$$
$$x_{53} = -99.4837673636768$$
$$x_{54} = -27.2271363311115$$
$$x_{55} = -5.23598775598299$$
$$x_{56} = 96.342174710087$$
$$x_{57} = -11.5191730631626$$
$$x_{58} = -83.7758040957278$$
$$x_{59} = -54.4542726622231$$
$$x_{60} = 3803.42150594604$$
$$x_{61} = 19.8967534727354$$
$$x_{62} = 48.1710873550435$$
$$x_{63} = -49.2182849062401$$
$$x_{64} = -10.471975511966$$
$$x_{65} = 4.18879020478639$$
$$x_{66} = 32.4631240870945$$
$$x_{67} = 11.5191730631626$$
$$x_{68} = 83.7758040957278$$
$$x_{69} = -42.9350995990605$$
$$x_{70} = -71.2094334813686$$
$$x_{71} = -19.8967534727354$$
$$x_{72} = 54.4542726622231$$
$$x_{73} = 99.4837673636768$$
$$x_{74} = 92.1533845053006$$
$$x_{75} = -48.1710873550435$$
$$x_{76} = 46.0766922526503$$
$$x_{77} = 24.0855436775217$$
$$x_{78} = 10.471975511966$$
$$x_{79} = 17.8023583703422$$
$$x_{80} = -17.8023583703422$$
$$x_{81} = -57.5958653158129$$
$$x_{82} = -92.1533845053006$$
$$x_{83} = -52.3598775598299$$
$$x_{84} = -98.4365698124802$$
Las raíces dadas
$$x_{31} = -673.348025419412$$
$$x_{53} = -99.4837673636768$$
$$x_{84} = -98.4365698124802$$
$$x_{25} = -96.342174710087$$
$$x_{1} = -93.2005820564972$$
$$x_{82} = -92.1533845053006$$
$$x_{29} = -90.0589894029074$$
$$x_{6} = -85.870199198121$$
$$x_{58} = -83.7758040957278$$
$$x_{3} = -79.5870138909414$$
$$x_{24} = -77.4926187885482$$
$$x_{13} = -76.4454212373516$$
$$x_{37} = -74.3510261349584$$
$$x_{70} = -71.2094334813686$$
$$x_{18} = -70.162235930172$$
$$x_{2} = -68.0678408277789$$
$$x_{16} = -63.8790506229925$$
$$x_{40} = -61.7846555205993$$
$$x_{52} = -60.7374579694027$$
$$x_{81} = -57.5958653158129$$
$$x_{43} = -55.5014702134197$$
$$x_{59} = -54.4542726622231$$
$$x_{83} = -52.3598775598299$$
$$x_{63} = -49.2182849062401$$
$$x_{75} = -48.1710873550435$$
$$x_{49} = -46.0766922526503$$
$$x_{69} = -42.9350995990605$$
$$x_{30} = -41.8879020478639$$
$$x_{23} = -39.7935069454707$$
$$x_{10} = -35.6047167406843$$
$$x_{50} = -33.5103216382911$$
$$x_{14} = -32.4631240870945$$
$$x_{44} = -30.3687289847013$$
$$x_{54} = -27.2271363311115$$
$$x_{46} = -26.1799387799149$$
$$x_{28} = -24.0855436775217$$
$$x_{71} = -19.8967534727354$$
$$x_{80} = -17.8023583703422$$
$$x_{42} = -13.6135681655558$$
$$x_{57} = -11.5191730631626$$
$$x_{64} = -10.471975511966$$
$$x_{55} = -5.23598775598299$$
$$x_{7} = -4.18879020478639$$
$$x_{35} = -2.0943951023932$$
$$x_{11} = 2.0943951023932$$
$$x_{65} = 4.18879020478639$$
$$x_{47} = 8.37758040957278$$
$$x_{78} = 10.471975511966$$
$$x_{67} = 11.5191730631626$$
$$x_{51} = 16.7551608191456$$
$$x_{79} = 17.8023583703422$$
$$x_{61} = 19.8967534727354$$
$$x_{77} = 24.0855436775217$$
$$x_{38} = 26.1799387799149$$
$$x_{15} = 30.3687289847013$$
$$x_{66} = 32.4631240870945$$
$$x_{12} = 33.5103216382911$$
$$x_{21} = 38.7463093942741$$
$$x_{17} = 39.7935069454707$$
$$x_{36} = 41.8879020478639$$
$$x_{76} = 46.0766922526503$$
$$x_{62} = 48.1710873550435$$
$$x_{48} = 52.3598775598299$$
$$x_{72} = 54.4542726622231$$
$$x_{39} = 55.5014702134197$$
$$x_{32} = 60.7374579694027$$
$$x_{9} = 61.7846555205993$$
$$x_{4} = 63.8790506229925$$
$$x_{41} = 68.0678408277789$$
$$x_{19} = 70.162235930172$$
$$x_{8} = 74.3510261349584$$
$$x_{22} = 76.4454212373516$$
$$x_{45} = 77.4926187885482$$
$$x_{5} = 82.7286065445312$$
$$x_{68} = 83.7758040957278$$
$$x_{26} = 85.870199198121$$
$$x_{33} = 90.0589894029074$$
$$x_{74} = 92.1533845053006$$
$$x_{56} = 96.342174710087$$
$$x_{27} = 98.4365698124802$$
$$x_{73} = 99.4837673636768$$
$$x_{20} = 269.129770657526$$
$$x_{34} = 275.412955964705$$
$$x_{60} = 3803.42150594604$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} < x_{31}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{31} - \frac{1}{10}$$
=
$$-673.348025419412 + - \frac{1}{10}$$
=
$$-673.448025419412$$
lo sustituimos en la expresión
$$\left|{\cos{\left(x \right)}}\right| < \frac{1}{2}$$
$$\left|{\cos{\left(-673.448025419412 \right)}}\right| < \frac{1}{2}$$
0.411043807676242 < 1/2

significa que una de las soluciones de nuestra ecuación será con:
$$x < -673.348025419412$$
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       x31      x53      x84      x25      x1      x82      x29      x6      x58      x3      x24      x13      x37      x70      x18      x2      x16      x40      x52      x81      x43      x59      x83      x63      x75      x49      x69      x30      x23      x10      x50      x14      x44      x54      x46      x28      x71      x80      x42      x57      x64      x55      x7      x35      x11      x65      x47      x78      x67      x51      x79      x61      x77      x38      x15      x66      x12      x21      x17      x36      x76      x62      x48      x72      x39      x32      x9      x4      x41      x19      x8      x22      x45      x5      x68      x26      x33      x74      x56      x27      x73      x20      x34      x60

Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x < -673.348025419412$$
$$x > -99.4837673636768 \wedge x < -98.4365698124802$$
$$x > -96.342174710087 \wedge x < -93.2005820564972$$
$$x > -92.1533845053006 \wedge x < -90.0589894029074$$
$$x > -85.870199198121 \wedge x < -83.7758040957278$$
$$x > -79.5870138909414 \wedge x < -77.4926187885482$$
$$x > -76.4454212373516 \wedge x < -74.3510261349584$$
$$x > -71.2094334813686 \wedge x < -70.162235930172$$
$$x > -68.0678408277789 \wedge x < -63.8790506229925$$
$$x > -61.7846555205993 \wedge x < -60.7374579694027$$
$$x > -57.5958653158129 \wedge x < -55.5014702134197$$
$$x > -54.4542726622231 \wedge x < -52.3598775598299$$
$$x > -49.2182849062401 \wedge x < -48.1710873550435$$
$$x > -46.0766922526503 \wedge x < -42.9350995990605$$
$$x > -41.8879020478639 \wedge x < -39.7935069454707$$
$$x > -35.6047167406843 \wedge x < -33.5103216382911$$
$$x > -32.4631240870945 \wedge x < -30.3687289847013$$
$$x > -27.2271363311115 \wedge x < -26.1799387799149$$
$$x > -24.0855436775217 \wedge x < -19.8967534727354$$
$$x > -17.8023583703422 \wedge x < -13.6135681655558$$
$$x > -11.5191730631626 \wedge x < -10.471975511966$$
$$x > -5.23598775598299 \wedge x < -4.18879020478639$$
$$x > -2.0943951023932 \wedge x < 2.0943951023932$$
$$x > 4.18879020478639 \wedge x < 8.37758040957278$$
$$x > 10.471975511966 \wedge x < 11.5191730631626$$
$$x > 16.7551608191456 \wedge x < 17.8023583703422$$
$$x > 19.8967534727354 \wedge x < 24.0855436775217$$
$$x > 26.1799387799149 \wedge x < 30.3687289847013$$
$$x > 32.4631240870945 \wedge x < 33.5103216382911$$
$$x > 38.7463093942741 \wedge x < 39.7935069454707$$
$$x > 41.8879020478639 \wedge x < 46.0766922526503$$
$$x > 48.1710873550435 \wedge x < 52.3598775598299$$
$$x > 54.4542726622231 \wedge x < 55.5014702134197$$
$$x > 60.7374579694027 \wedge x < 61.7846555205993$$
$$x > 63.8790506229925 \wedge x < 68.0678408277789$$
$$x > 70.162235930172 \wedge x < 74.3510261349584$$
$$x > 76.4454212373516 \wedge x < 77.4926187885482$$
$$x > 82.7286065445312 \wedge x < 83.7758040957278$$
$$x > 85.870199198121 \wedge x < 90.0589894029074$$
$$x > 92.1533845053006 \wedge x < 96.342174710087$$
$$x > 98.4365698124802 \wedge x < 99.4837673636768$$
$$x > 269.129770657526 \wedge x < 275.412955964705$$
$$x > 3803.42150594604$$
Solución de la desigualdad en el gráfico