Se da la desigualdad:
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} > -2$$
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} = -2$$
Resolvemos:
Tenemos la ecuación
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} = -2$$
cambiamos
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} + 2 = 0$$
$$- 2 \sin^{2}{\left(x \right)} + 5 \sin{\left(x \right)} + 3 = 0$$
Sustituimos
$$w = \sin{\left(x \right)}$$
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
$$a = -2$$
$$b = 5$$
$$c = 3$$
, entonces
D = b^2 - 4 * a * c =
(5)^2 - 4 * (-2) * (3) = 49
Como D > 0 la ecuación tiene dos raíces.
w1 = (-b + sqrt(D)) / (2*a)
w2 = (-b - sqrt(D)) / (2*a)
o
$$w_{1} = - \frac{1}{2}$$
$$w_{2} = 3$$
hacemos cambio inverso
$$\sin{\left(x \right)} = w$$
Tenemos la ecuación
$$\sin{\left(x \right)} = w$$
es la ecuación trigonométrica más simple
Esta ecuación se reorganiza en
$$x = 2 \pi n + \operatorname{asin}{\left(w \right)}$$
$$x = 2 \pi n - \operatorname{asin}{\left(w \right)} + \pi$$
O
$$x = 2 \pi n + \operatorname{asin}{\left(w \right)}$$
$$x = 2 \pi n - \operatorname{asin}{\left(w \right)} + \pi$$
, donde n es cualquier número entero
sustituimos w:
$$x_{1} = 2 \pi n + \operatorname{asin}{\left(w_{1} \right)}$$
$$x_{1} = 2 \pi n + \operatorname{asin}{\left(- \frac{1}{2} \right)}$$
$$x_{1} = 2 \pi n - \frac{\pi}{6}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(w_{2} \right)}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(3 \right)}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(3 \right)}$$
$$x_{3} = 2 \pi n - \operatorname{asin}{\left(w_{1} \right)} + \pi$$
$$x_{3} = 2 \pi n - \operatorname{asin}{\left(- \frac{1}{2} \right)} + \pi$$
$$x_{3} = 2 \pi n + \frac{7 \pi}{6}$$
$$x_{4} = 2 \pi n - \operatorname{asin}{\left(w_{2} \right)} + \pi$$
$$x_{4} = 2 \pi n + \pi - \operatorname{asin}{\left(3 \right)}$$
$$x_{4} = 2 \pi n + \pi - \operatorname{asin}{\left(3 \right)}$$
$$x_{1} = 47.6474885794452$$
$$x_{2} = 74.8746249105567$$
$$x_{3} = 81.1578102177363$$
$$x_{4} = -27.7507351067098$$
$$x_{5} = 60.2138591938044$$
$$x_{6} = 110.479341651241$$
$$x_{7} = -19.3731546971371$$
$$x_{8} = -50.789081233035$$
$$x_{9} = -21.4675497995303$$
$$x_{10} = 112.573736753634$$
$$x_{11} = -44.5058959258554$$
$$x_{12} = -57.0722665402146$$
$$x_{13} = 43.4586983746588$$
$$x_{14} = 18.3259571459405$$
$$x_{15} = -643.502895210309$$
$$x_{16} = -34.0339204138894$$
$$x_{17} = -38.2227106186758$$
$$x_{18} = -59.1666616426078$$
$$x_{19} = 72.7802298081635$$
$$x_{20} = -13.0899693899575$$
$$x_{21} = 3.66519142918809$$
$$x_{22} = -6.80678408277789$$
$$x_{23} = -52.8834763354282$$
$$x_{24} = -65.4498469497874$$
$$x_{25} = -46.6002910282486$$
$$x_{26} = 87.4409955249159$$
$$x_{27} = -88.4881930761125$$
$$x_{28} = 24.60914245312$$
$$x_{29} = 100.007366139275$$
$$x_{30} = -31.9395253114962$$
$$x_{31} = 79.0634151153431$$
$$x_{32} = -63.3554518473942$$
$$x_{33} = 56.025068989018$$
$$x_{34} = 41.3643032722656$$
$$x_{35} = 91.6297857297023$$
$$x_{36} = 28.7979326579064$$
$$x_{37} = 93.7241808320955$$
$$x_{38} = -69.6386371545737$$
$$x_{39} = -45867.7763411866$$
$$x_{40} = 37.1755130674792$$
$$x_{41} = 53.9306738866248$$
$$x_{42} = 16.2315620435473$$
$$x_{43} = -75.9218224617533$$
$$x_{44} = -94.7713783832921$$
$$x_{45} = -78.0162175641465$$
$$x_{46} = 791.15774992903$$
$$x_{47} = 68.5914396033772$$
$$x_{48} = -82.2050077689329$$
$$x_{49} = -96.8657734856853$$
$$x_{50} = -84.2994028713261$$
$$x_{51} = 9.94837673636768$$
$$x_{52} = -0.523598775598299$$
$$x_{53} = 12.0427718387609$$
$$x_{54} = -2.61799387799149$$
$$x_{55} = 49.7418836818384$$
$$x_{56} = -71.733032256967$$
$$x_{57} = -40.317105721069$$
$$x_{58} = -8.90117918517108$$
$$x_{59} = 66.497044500984$$
$$x_{60} = 35.081117965086$$
$$x_{61} = 85.3466004225227$$
$$x_{62} = 5.75958653158129$$
$$x_{63} = -90.5825881785057$$
$$x_{64} = -239.284640448423$$
$$x_{65} = -25.6563400043166$$
$$x_{66} = 22.5147473507269$$
$$x_{67} = -101.054563690472$$
$$x_{68} = -15.1843644923507$$
$$x_{69} = 62.3082542961976$$
$$x_{70} = 30.8923277602996$$
$$x_{71} = 97.9129710368819$$
$$x_{1} = 47.6474885794452$$
$$x_{2} = 74.8746249105567$$
$$x_{3} = 81.1578102177363$$
$$x_{4} = -27.7507351067098$$
$$x_{5} = 60.2138591938044$$
$$x_{6} = 110.479341651241$$
$$x_{7} = -19.3731546971371$$
$$x_{8} = -50.789081233035$$
$$x_{9} = -21.4675497995303$$
$$x_{10} = 112.573736753634$$
$$x_{11} = -44.5058959258554$$
$$x_{12} = -57.0722665402146$$
$$x_{13} = 43.4586983746588$$
$$x_{14} = 18.3259571459405$$
$$x_{15} = -643.502895210309$$
$$x_{16} = -34.0339204138894$$
$$x_{17} = -38.2227106186758$$
$$x_{18} = -59.1666616426078$$
$$x_{19} = 72.7802298081635$$
$$x_{20} = -13.0899693899575$$
$$x_{21} = 3.66519142918809$$
$$x_{22} = -6.80678408277789$$
$$x_{23} = -52.8834763354282$$
$$x_{24} = -65.4498469497874$$
$$x_{25} = -46.6002910282486$$
$$x_{26} = 87.4409955249159$$
$$x_{27} = -88.4881930761125$$
$$x_{28} = 24.60914245312$$
$$x_{29} = 100.007366139275$$
$$x_{30} = -31.9395253114962$$
$$x_{31} = 79.0634151153431$$
$$x_{32} = -63.3554518473942$$
$$x_{33} = 56.025068989018$$
$$x_{34} = 41.3643032722656$$
$$x_{35} = 91.6297857297023$$
$$x_{36} = 28.7979326579064$$
$$x_{37} = 93.7241808320955$$
$$x_{38} = -69.6386371545737$$
$$x_{39} = -45867.7763411866$$
$$x_{40} = 37.1755130674792$$
$$x_{41} = 53.9306738866248$$
$$x_{42} = 16.2315620435473$$
$$x_{43} = -75.9218224617533$$
$$x_{44} = -94.7713783832921$$
$$x_{45} = -78.0162175641465$$
$$x_{46} = 791.15774992903$$
$$x_{47} = 68.5914396033772$$
$$x_{48} = -82.2050077689329$$
$$x_{49} = -96.8657734856853$$
$$x_{50} = -84.2994028713261$$
$$x_{51} = 9.94837673636768$$
$$x_{52} = -0.523598775598299$$
$$x_{53} = 12.0427718387609$$
$$x_{54} = -2.61799387799149$$
$$x_{55} = 49.7418836818384$$
$$x_{56} = -71.733032256967$$
$$x_{57} = -40.317105721069$$
$$x_{58} = -8.90117918517108$$
$$x_{59} = 66.497044500984$$
$$x_{60} = 35.081117965086$$
$$x_{61} = 85.3466004225227$$
$$x_{62} = 5.75958653158129$$
$$x_{63} = -90.5825881785057$$
$$x_{64} = -239.284640448423$$
$$x_{65} = -25.6563400043166$$
$$x_{66} = 22.5147473507269$$
$$x_{67} = -101.054563690472$$
$$x_{68} = -15.1843644923507$$
$$x_{69} = 62.3082542961976$$
$$x_{70} = 30.8923277602996$$
$$x_{71} = 97.9129710368819$$
Las raíces dadas
$$x_{39} = -45867.7763411866$$
$$x_{15} = -643.502895210309$$
$$x_{64} = -239.284640448423$$
$$x_{67} = -101.054563690472$$
$$x_{49} = -96.8657734856853$$
$$x_{44} = -94.7713783832921$$
$$x_{63} = -90.5825881785057$$
$$x_{27} = -88.4881930761125$$
$$x_{50} = -84.2994028713261$$
$$x_{48} = -82.2050077689329$$
$$x_{45} = -78.0162175641465$$
$$x_{43} = -75.9218224617533$$
$$x_{56} = -71.733032256967$$
$$x_{38} = -69.6386371545737$$
$$x_{24} = -65.4498469497874$$
$$x_{32} = -63.3554518473942$$
$$x_{18} = -59.1666616426078$$
$$x_{12} = -57.0722665402146$$
$$x_{23} = -52.8834763354282$$
$$x_{8} = -50.789081233035$$
$$x_{25} = -46.6002910282486$$
$$x_{11} = -44.5058959258554$$
$$x_{57} = -40.317105721069$$
$$x_{17} = -38.2227106186758$$
$$x_{16} = -34.0339204138894$$
$$x_{30} = -31.9395253114962$$
$$x_{4} = -27.7507351067098$$
$$x_{65} = -25.6563400043166$$
$$x_{9} = -21.4675497995303$$
$$x_{7} = -19.3731546971371$$
$$x_{68} = -15.1843644923507$$
$$x_{20} = -13.0899693899575$$
$$x_{58} = -8.90117918517108$$
$$x_{22} = -6.80678408277789$$
$$x_{54} = -2.61799387799149$$
$$x_{52} = -0.523598775598299$$
$$x_{21} = 3.66519142918809$$
$$x_{62} = 5.75958653158129$$
$$x_{51} = 9.94837673636768$$
$$x_{53} = 12.0427718387609$$
$$x_{42} = 16.2315620435473$$
$$x_{14} = 18.3259571459405$$
$$x_{66} = 22.5147473507269$$
$$x_{28} = 24.60914245312$$
$$x_{36} = 28.7979326579064$$
$$x_{70} = 30.8923277602996$$
$$x_{60} = 35.081117965086$$
$$x_{40} = 37.1755130674792$$
$$x_{34} = 41.3643032722656$$
$$x_{13} = 43.4586983746588$$
$$x_{1} = 47.6474885794452$$
$$x_{55} = 49.7418836818384$$
$$x_{41} = 53.9306738866248$$
$$x_{33} = 56.025068989018$$
$$x_{5} = 60.2138591938044$$
$$x_{69} = 62.3082542961976$$
$$x_{59} = 66.497044500984$$
$$x_{47} = 68.5914396033772$$
$$x_{19} = 72.7802298081635$$
$$x_{2} = 74.8746249105567$$
$$x_{31} = 79.0634151153431$$
$$x_{3} = 81.1578102177363$$
$$x_{61} = 85.3466004225227$$
$$x_{26} = 87.4409955249159$$
$$x_{35} = 91.6297857297023$$
$$x_{37} = 93.7241808320955$$
$$x_{71} = 97.9129710368819$$
$$x_{29} = 100.007366139275$$
$$x_{6} = 110.479341651241$$
$$x_{10} = 112.573736753634$$
$$x_{46} = 791.15774992903$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} < x_{39}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{39} - \frac{1}{10}$$
=
$$-45867.7763411866 + - \frac{1}{10}$$
=
$$-45867.8763411866$$
lo sustituimos en la expresión
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} > -2$$
$$5 \sin{\left(-45867.8763411866 \right)} + \cos{\left(\left(-45867.8763411866\right) 2 \right)} > -2$$
-2.60182118651354 > -2
Entonces
$$x < -45867.7763411866$$
no se cumple
significa que una de las soluciones de nuestra ecuación será con:
$$x > -45867.7763411866 \wedge x < -643.502895210309$$
_____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
/ \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ /
-------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-------ο-------ο-------ο-------ο-------
x39 x15 x64 x67 x49 x44 x63 x27 x50 x48 x45 x43 x56 x38 x24 x32 x18 x12 x23 x8 x25 x11 x57 x17 x16 x30 x4 x65 x9 x7 x68 x20 x58 x22 x54 x52 x21 x62 x51 x53 x42 x14 x66 x28 x36 x70 x60 x40 x34 x13 x1 x55 x41 x33 x5 x69 x59 x47 x19 x2 x31 x3 x61 x26 x35 x37 x71 x29 x6 x10 x46
Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x > -45867.7763411866 \wedge x < -643.502895210309$$
$$x > -239.284640448423 \wedge x < -101.054563690472$$
$$x > -96.8657734856853 \wedge x < -94.7713783832921$$
$$x > -90.5825881785057 \wedge x < -88.4881930761125$$
$$x > -84.2994028713261 \wedge x < -82.2050077689329$$
$$x > -78.0162175641465 \wedge x < -75.9218224617533$$
$$x > -71.733032256967 \wedge x < -69.6386371545737$$
$$x > -65.4498469497874 \wedge x < -63.3554518473942$$
$$x > -59.1666616426078 \wedge x < -57.0722665402146$$
$$x > -52.8834763354282 \wedge x < -50.789081233035$$
$$x > -46.6002910282486 \wedge x < -44.5058959258554$$
$$x > -40.317105721069 \wedge x < -38.2227106186758$$
$$x > -34.0339204138894 \wedge x < -31.9395253114962$$
$$x > -27.7507351067098 \wedge x < -25.6563400043166$$
$$x > -21.4675497995303 \wedge x < -19.3731546971371$$
$$x > -15.1843644923507 \wedge x < -13.0899693899575$$
$$x > -8.90117918517108 \wedge x < -6.80678408277789$$
$$x > -2.61799387799149 \wedge x < -0.523598775598299$$
$$x > 3.66519142918809 \wedge x < 5.75958653158129$$
$$x > 9.94837673636768 \wedge x < 12.0427718387609$$
$$x > 16.2315620435473 \wedge x < 18.3259571459405$$
$$x > 22.5147473507269 \wedge x < 24.60914245312$$
$$x > 28.7979326579064 \wedge x < 30.8923277602996$$
$$x > 35.081117965086 \wedge x < 37.1755130674792$$
$$x > 41.3643032722656 \wedge x < 43.4586983746588$$
$$x > 47.6474885794452 \wedge x < 49.7418836818384$$
$$x > 53.9306738866248 \wedge x < 56.025068989018$$
$$x > 60.2138591938044 \wedge x < 62.3082542961976$$
$$x > 66.497044500984 \wedge x < 68.5914396033772$$
$$x > 72.7802298081635 \wedge x < 74.8746249105567$$
$$x > 79.0634151153431 \wedge x < 81.1578102177363$$
$$x > 85.3466004225227 \wedge x < 87.4409955249159$$
$$x > 91.6297857297023 \wedge x < 93.7241808320955$$
$$x > 97.9129710368819 \wedge x < 100.007366139275$$
$$x > 110.479341651241 \wedge x < 112.573736753634$$
$$x > 791.15774992903$$