Se da la desigualdad:
$$\cos{\left(t \right)} < \frac{2}{3}$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$\cos{\left(t \right)} = \frac{2}{3}$$
Resolvemos:
Tenemos la ecuación
$$\cos{\left(t \right)} = \frac{2}{3}$$
cambiamos
$$\cos{\left(t \right)} - \frac{2}{3} = 0$$
$$\cos{\left(t \right)} - \frac{2}{3} = 0$$
Sustituimos
$$w = \cos{\left(t \right)}$$
Transportamos los términos libres (sin w)
del miembro izquierdo al derecho, obtenemos:
$$w = \frac{2}{3}$$
Obtenemos la respuesta: w = 2/3
hacemos cambio inverso
$$\cos{\left(t \right)} = w$$
sustituimos w:
$$x_{1} = -25.9738098992863$$
$$x_{2} = 80.8403403227667$$
$$x_{3} = -49.4244137868688$$
$$x_{4} = -5.44211663661166$$
$$x_{5} = -80.8403403227667$$
$$x_{6} = -11.7253019437912$$
$$x_{7} = -82.5224776639025$$
$$x_{8} = -7.12425397774752$$
$$x_{9} = 18.0084872509708$$
$$x_{10} = -57.3897364351842$$
$$x_{11} = -51.1065511280046$$
$$x_{12} = 82.5224776639025$$
$$x_{13} = -13.4074392849271$$
$$x_{14} = 13.4074392849271$$
$$x_{15} = -19.6906245921067$$
$$x_{16} = -44.823365820825$$
$$x_{17} = 19.6906245921067$$
$$x_{18} = 25.9738098992863$$
$$x_{19} = -55.7075990940483$$
$$x_{20} = 38.5401805136454$$
$$x_{21} = 69.9561070495434$$
$$x_{22} = 49.4244137868688$$
$$x_{23} = -74.5571550155871$$
$$x_{24} = 63.6729217423638$$
$$x_{25} = -69.9561070495434$$
$$x_{26} = -32.2569952064659$$
$$x_{27} = -38.5401805136454$$
$$x_{28} = 5.44211663661166$$
$$x_{29} = 44.823365820825$$
$$x_{30} = 76.239292356723$$
$$x_{31} = 57.3897364351842$$
$$x_{32} = -18.0084872509708$$
$$x_{33} = -101.372033585441$$
$$x_{34} = 74.5571550155871$$
$$x_{35} = 99.6898962443055$$
$$x_{36} = 87.1235256299463$$
$$x_{37} = 11.7253019437912$$
$$x_{38} = -68.2739697084075$$
$$x_{39} = 43.1412284796892$$
$$x_{40} = -0.84106867056793$$
$$x_{41} = 0.84106867056793$$
$$x_{42} = -87.1235256299463$$
$$x_{43} = 61.9907844012279$$
$$x_{44} = -36.8580431725096$$
$$x_{45} = -63.6729217423638$$
$$x_{46} = 88.8056629710821$$
$$x_{47} = -95.0888482782617$$
$$x_{48} = 32.2569952064659$$
$$x_{49} = -93.4067109371259$$
$$x_{50} = -43.1412284796892$$
$$x_{51} = -99.6898962443055$$
$$x_{52} = 68.2739697084075$$
$$x_{53} = -61.9907844012279$$
$$x_{54} = -24.2916725581504$$
$$x_{55} = 36.8580431725096$$
$$x_{56} = 51.1065511280046$$
$$x_{57} = 24.2916725581504$$
$$x_{58} = -88.8056629710821$$
$$x_{59} = 30.57485786533$$
$$x_{60} = -76.239292356723$$
$$x_{61} = 93.4067109371259$$
$$x_{62} = 7.12425397774752$$
$$x_{63} = 55.7075990940483$$
$$x_{64} = 95.0888482782617$$
$$x_{65} = -30.57485786533$$
$$x_{1} = -25.9738098992863$$
$$x_{2} = 80.8403403227667$$
$$x_{3} = -49.4244137868688$$
$$x_{4} = -5.44211663661166$$
$$x_{5} = -80.8403403227667$$
$$x_{6} = -11.7253019437912$$
$$x_{7} = -82.5224776639025$$
$$x_{8} = -7.12425397774752$$
$$x_{9} = 18.0084872509708$$
$$x_{10} = -57.3897364351842$$
$$x_{11} = -51.1065511280046$$
$$x_{12} = 82.5224776639025$$
$$x_{13} = -13.4074392849271$$
$$x_{14} = 13.4074392849271$$
$$x_{15} = -19.6906245921067$$
$$x_{16} = -44.823365820825$$
$$x_{17} = 19.6906245921067$$
$$x_{18} = 25.9738098992863$$
$$x_{19} = -55.7075990940483$$
$$x_{20} = 38.5401805136454$$
$$x_{21} = 69.9561070495434$$
$$x_{22} = 49.4244137868688$$
$$x_{23} = -74.5571550155871$$
$$x_{24} = 63.6729217423638$$
$$x_{25} = -69.9561070495434$$
$$x_{26} = -32.2569952064659$$
$$x_{27} = -38.5401805136454$$
$$x_{28} = 5.44211663661166$$
$$x_{29} = 44.823365820825$$
$$x_{30} = 76.239292356723$$
$$x_{31} = 57.3897364351842$$
$$x_{32} = -18.0084872509708$$
$$x_{33} = -101.372033585441$$
$$x_{34} = 74.5571550155871$$
$$x_{35} = 99.6898962443055$$
$$x_{36} = 87.1235256299463$$
$$x_{37} = 11.7253019437912$$
$$x_{38} = -68.2739697084075$$
$$x_{39} = 43.1412284796892$$
$$x_{40} = -0.84106867056793$$
$$x_{41} = 0.84106867056793$$
$$x_{42} = -87.1235256299463$$
$$x_{43} = 61.9907844012279$$
$$x_{44} = -36.8580431725096$$
$$x_{45} = -63.6729217423638$$
$$x_{46} = 88.8056629710821$$
$$x_{47} = -95.0888482782617$$
$$x_{48} = 32.2569952064659$$
$$x_{49} = -93.4067109371259$$
$$x_{50} = -43.1412284796892$$
$$x_{51} = -99.6898962443055$$
$$x_{52} = 68.2739697084075$$
$$x_{53} = -61.9907844012279$$
$$x_{54} = -24.2916725581504$$
$$x_{55} = 36.8580431725096$$
$$x_{56} = 51.1065511280046$$
$$x_{57} = 24.2916725581504$$
$$x_{58} = -88.8056629710821$$
$$x_{59} = 30.57485786533$$
$$x_{60} = -76.239292356723$$
$$x_{61} = 93.4067109371259$$
$$x_{62} = 7.12425397774752$$
$$x_{63} = 55.7075990940483$$
$$x_{64} = 95.0888482782617$$
$$x_{65} = -30.57485786533$$
Las raíces dadas
$$x_{33} = -101.372033585441$$
$$x_{51} = -99.6898962443055$$
$$x_{47} = -95.0888482782617$$
$$x_{49} = -93.4067109371259$$
$$x_{58} = -88.8056629710821$$
$$x_{42} = -87.1235256299463$$
$$x_{7} = -82.5224776639025$$
$$x_{5} = -80.8403403227667$$
$$x_{60} = -76.239292356723$$
$$x_{23} = -74.5571550155871$$
$$x_{25} = -69.9561070495434$$
$$x_{38} = -68.2739697084075$$
$$x_{45} = -63.6729217423638$$
$$x_{53} = -61.9907844012279$$
$$x_{10} = -57.3897364351842$$
$$x_{19} = -55.7075990940483$$
$$x_{11} = -51.1065511280046$$
$$x_{3} = -49.4244137868688$$
$$x_{16} = -44.823365820825$$
$$x_{50} = -43.1412284796892$$
$$x_{27} = -38.5401805136454$$
$$x_{44} = -36.8580431725096$$
$$x_{26} = -32.2569952064659$$
$$x_{65} = -30.57485786533$$
$$x_{1} = -25.9738098992863$$
$$x_{54} = -24.2916725581504$$
$$x_{15} = -19.6906245921067$$
$$x_{32} = -18.0084872509708$$
$$x_{13} = -13.4074392849271$$
$$x_{6} = -11.7253019437912$$
$$x_{8} = -7.12425397774752$$
$$x_{4} = -5.44211663661166$$
$$x_{40} = -0.84106867056793$$
$$x_{41} = 0.84106867056793$$
$$x_{28} = 5.44211663661166$$
$$x_{62} = 7.12425397774752$$
$$x_{37} = 11.7253019437912$$
$$x_{14} = 13.4074392849271$$
$$x_{9} = 18.0084872509708$$
$$x_{17} = 19.6906245921067$$
$$x_{57} = 24.2916725581504$$
$$x_{18} = 25.9738098992863$$
$$x_{59} = 30.57485786533$$
$$x_{48} = 32.2569952064659$$
$$x_{55} = 36.8580431725096$$
$$x_{20} = 38.5401805136454$$
$$x_{39} = 43.1412284796892$$
$$x_{29} = 44.823365820825$$
$$x_{22} = 49.4244137868688$$
$$x_{56} = 51.1065511280046$$
$$x_{63} = 55.7075990940483$$
$$x_{31} = 57.3897364351842$$
$$x_{43} = 61.9907844012279$$
$$x_{24} = 63.6729217423638$$
$$x_{52} = 68.2739697084075$$
$$x_{21} = 69.9561070495434$$
$$x_{34} = 74.5571550155871$$
$$x_{30} = 76.239292356723$$
$$x_{2} = 80.8403403227667$$
$$x_{12} = 82.5224776639025$$
$$x_{36} = 87.1235256299463$$
$$x_{46} = 88.8056629710821$$
$$x_{61} = 93.4067109371259$$
$$x_{64} = 95.0888482782617$$
$$x_{35} = 99.6898962443055$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} < x_{33}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{33} - \frac{1}{10}$$
=
$$-101.372033585441 + - \frac{1}{10}$$
=
$$-101.472033585441$$
lo sustituimos en la expresión
$$\cos{\left(t \right)} < \frac{2}{3}$$
$$\cos{\left(t \right)} < \frac{2}{3}$$
cos(t) < 2/3
Entonces
$$x < -101.372033585441$$
no se cumple
significa que una de las soluciones de nuestra ecuación será con:
$$x > -101.372033585441 \wedge x < -99.6898962443055$$
_____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
/ \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ /
-------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-------
x33 x51 x47 x49 x58 x42 x7 x5 x60 x23 x25 x38 x45 x53 x10 x19 x11 x3 x16 x50 x27 x44 x26 x65 x1 x54 x15 x32 x13 x6 x8 x4 x40 x41 x28 x62 x37 x14 x9 x17 x57 x18 x59 x48 x55 x20 x39 x29 x22 x56 x63 x31 x43 x24 x52 x21 x34 x30 x2 x12 x36 x46 x61 x64 x35
Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x > -101.372033585441 \wedge x < -99.6898962443055$$
$$x > -95.0888482782617 \wedge x < -93.4067109371259$$
$$x > -88.8056629710821 \wedge x < -87.1235256299463$$
$$x > -82.5224776639025 \wedge x < -80.8403403227667$$
$$x > -76.239292356723 \wedge x < -74.5571550155871$$
$$x > -69.9561070495434 \wedge x < -68.2739697084075$$
$$x > -63.6729217423638 \wedge x < -61.9907844012279$$
$$x > -57.3897364351842 \wedge x < -55.7075990940483$$
$$x > -51.1065511280046 \wedge x < -49.4244137868688$$
$$x > -44.823365820825 \wedge x < -43.1412284796892$$
$$x > -38.5401805136454 \wedge x < -36.8580431725096$$
$$x > -32.2569952064659 \wedge x < -30.57485786533$$
$$x > -25.9738098992863 \wedge x < -24.2916725581504$$
$$x > -19.6906245921067 \wedge x < -18.0084872509708$$
$$x > -13.4074392849271 \wedge x < -11.7253019437912$$
$$x > -7.12425397774752 \wedge x < -5.44211663661166$$
$$x > -0.84106867056793 \wedge x < 0.84106867056793$$
$$x > 5.44211663661166 \wedge x < 7.12425397774752$$
$$x > 11.7253019437912 \wedge x < 13.4074392849271$$
$$x > 18.0084872509708 \wedge x < 19.6906245921067$$
$$x > 24.2916725581504 \wedge x < 25.9738098992863$$
$$x > 30.57485786533 \wedge x < 32.2569952064659$$
$$x > 36.8580431725096 \wedge x < 38.5401805136454$$
$$x > 43.1412284796892 \wedge x < 44.823365820825$$
$$x > 49.4244137868688 \wedge x < 51.1065511280046$$
$$x > 55.7075990940483 \wedge x < 57.3897364351842$$
$$x > 61.9907844012279 \wedge x < 63.6729217423638$$
$$x > 68.2739697084075 \wedge x < 69.9561070495434$$
$$x > 74.5571550155871 \wedge x < 76.239292356723$$
$$x > 80.8403403227667 \wedge x < 82.5224776639025$$
$$x > 87.1235256299463 \wedge x < 88.8056629710821$$
$$x > 93.4067109371259 \wedge x < 95.0888482782617$$
$$x > 99.6898962443055$$