Sr Examen

cos2x+5sinx<=-2 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
cos(2*x) + 5*sin(x) <= -2
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} \leq -2$$
5*sin(x) + cos(2*x) <= -2
Solución detallada
Se da la desigualdad:
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} \leq -2$$
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:
$$x_{1} = 2 \pi n + \operatorname{asin}{\left(w_{1} \right)}$$
$$x_{1} = 2 \pi n + \operatorname{asin}{\left(- \frac{1}{2} \right)}$$
$$x_{1} = 2 \pi n - \frac{\pi}{6}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(w_{2} \right)}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(3 \right)}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(3 \right)}$$
$$x_{3} = 2 \pi n - \operatorname{asin}{\left(w_{1} \right)} + \pi$$
$$x_{3} = 2 \pi n - \operatorname{asin}{\left(- \frac{1}{2} \right)} + \pi$$
$$x_{3} = 2 \pi n + \frac{7 \pi}{6}$$
$$x_{4} = 2 \pi n - \operatorname{asin}{\left(w_{2} \right)} + \pi$$
$$x_{4} = 2 \pi n + \pi - \operatorname{asin}{\left(3 \right)}$$
$$x_{4} = 2 \pi n + \pi - \operatorname{asin}{\left(3 \right)}$$
$$x_{1} = -75.9218224617533$$
$$x_{2} = -90.5825881785057$$
$$x_{3} = 30.8923277602996$$
$$x_{4} = -96.8657734856853$$
$$x_{5} = -65.4498469497874$$
$$x_{6} = -15.1843644923507$$
$$x_{7} = -38.2227106186758$$
$$x_{8} = -84.2994028713261$$
$$x_{9} = -45867.7763411866$$
$$x_{10} = 9.94837673636768$$
$$x_{11} = -34.0339204138894$$
$$x_{12} = 110.479341651241$$
$$x_{13} = 66.497044500984$$
$$x_{14} = -21.4675497995303$$
$$x_{15} = -57.0722665402146$$
$$x_{16} = -40.317105721069$$
$$x_{17} = 35.081117965086$$
$$x_{18} = -2.61799387799149$$
$$x_{19} = 18.3259571459405$$
$$x_{20} = -0.523598775598299$$
$$x_{21} = -44.5058959258554$$
$$x_{22} = 53.9306738866248$$
$$x_{23} = -94.7713783832921$$
$$x_{24} = -82.2050077689329$$
$$x_{25} = -52.8834763354282$$
$$x_{26} = -25.6563400043166$$
$$x_{27} = -6.80678408277789$$
$$x_{28} = -643.502895210309$$
$$x_{29} = 16.2315620435473$$
$$x_{30} = 41.3643032722656$$
$$x_{31} = 79.0634151153431$$
$$x_{32} = -101.054563690472$$
$$x_{33} = 74.8746249105567$$
$$x_{34} = 37.1755130674792$$
$$x_{35} = -46.6002910282486$$
$$x_{36} = -78.0162175641465$$
$$x_{37} = 22.5147473507269$$
$$x_{38} = 12.0427718387609$$
$$x_{39} = 47.6474885794452$$
$$x_{40} = 24.60914245312$$
$$x_{41} = 112.573736753634$$
$$x_{42} = 91.6297857297023$$
$$x_{43} = -88.4881930761125$$
$$x_{44} = -8.90117918517108$$
$$x_{45} = -50.789081233035$$
$$x_{46} = 72.7802298081635$$
$$x_{47} = 49.7418836818384$$
$$x_{48} = 60.2138591938044$$
$$x_{49} = 43.4586983746588$$
$$x_{50} = 28.7979326579064$$
$$x_{51} = 62.3082542961976$$
$$x_{52} = -239.284640448423$$
$$x_{53} = -59.1666616426078$$
$$x_{54} = 68.5914396033772$$
$$x_{55} = -71.733032256967$$
$$x_{56} = -13.0899693899575$$
$$x_{57} = 100.007366139275$$
$$x_{58} = 791.15774992903$$
$$x_{59} = -19.3731546971371$$
$$x_{60} = -69.6386371545737$$
$$x_{61} = 93.7241808320955$$
$$x_{62} = 3.66519142918809$$
$$x_{63} = 97.9129710368819$$
$$x_{64} = -27.7507351067098$$
$$x_{65} = 81.1578102177363$$
$$x_{66} = -63.3554518473942$$
$$x_{67} = 56.025068989018$$
$$x_{68} = 87.4409955249159$$
$$x_{69} = -31.9395253114962$$
$$x_{70} = 5.75958653158129$$
$$x_{71} = 85.3466004225227$$
$$x_{1} = -75.9218224617533$$
$$x_{2} = -90.5825881785057$$
$$x_{3} = 30.8923277602996$$
$$x_{4} = -96.8657734856853$$
$$x_{5} = -65.4498469497874$$
$$x_{6} = -15.1843644923507$$
$$x_{7} = -38.2227106186758$$
$$x_{8} = -84.2994028713261$$
$$x_{9} = -45867.7763411866$$
$$x_{10} = 9.94837673636768$$
$$x_{11} = -34.0339204138894$$
$$x_{12} = 110.479341651241$$
$$x_{13} = 66.497044500984$$
$$x_{14} = -21.4675497995303$$
$$x_{15} = -57.0722665402146$$
$$x_{16} = -40.317105721069$$
$$x_{17} = 35.081117965086$$
$$x_{18} = -2.61799387799149$$
$$x_{19} = 18.3259571459405$$
$$x_{20} = -0.523598775598299$$
$$x_{21} = -44.5058959258554$$
$$x_{22} = 53.9306738866248$$
$$x_{23} = -94.7713783832921$$
$$x_{24} = -82.2050077689329$$
$$x_{25} = -52.8834763354282$$
$$x_{26} = -25.6563400043166$$
$$x_{27} = -6.80678408277789$$
$$x_{28} = -643.502895210309$$
$$x_{29} = 16.2315620435473$$
$$x_{30} = 41.3643032722656$$
$$x_{31} = 79.0634151153431$$
$$x_{32} = -101.054563690472$$
$$x_{33} = 74.8746249105567$$
$$x_{34} = 37.1755130674792$$
$$x_{35} = -46.6002910282486$$
$$x_{36} = -78.0162175641465$$
$$x_{37} = 22.5147473507269$$
$$x_{38} = 12.0427718387609$$
$$x_{39} = 47.6474885794452$$
$$x_{40} = 24.60914245312$$
$$x_{41} = 112.573736753634$$
$$x_{42} = 91.6297857297023$$
$$x_{43} = -88.4881930761125$$
$$x_{44} = -8.90117918517108$$
$$x_{45} = -50.789081233035$$
$$x_{46} = 72.7802298081635$$
$$x_{47} = 49.7418836818384$$
$$x_{48} = 60.2138591938044$$
$$x_{49} = 43.4586983746588$$
$$x_{50} = 28.7979326579064$$
$$x_{51} = 62.3082542961976$$
$$x_{52} = -239.284640448423$$
$$x_{53} = -59.1666616426078$$
$$x_{54} = 68.5914396033772$$
$$x_{55} = -71.733032256967$$
$$x_{56} = -13.0899693899575$$
$$x_{57} = 100.007366139275$$
$$x_{58} = 791.15774992903$$
$$x_{59} = -19.3731546971371$$
$$x_{60} = -69.6386371545737$$
$$x_{61} = 93.7241808320955$$
$$x_{62} = 3.66519142918809$$
$$x_{63} = 97.9129710368819$$
$$x_{64} = -27.7507351067098$$
$$x_{65} = 81.1578102177363$$
$$x_{66} = -63.3554518473942$$
$$x_{67} = 56.025068989018$$
$$x_{68} = 87.4409955249159$$
$$x_{69} = -31.9395253114962$$
$$x_{70} = 5.75958653158129$$
$$x_{71} = 85.3466004225227$$
Las raíces dadas
$$x_{9} = -45867.7763411866$$
$$x_{28} = -643.502895210309$$
$$x_{52} = -239.284640448423$$
$$x_{32} = -101.054563690472$$
$$x_{4} = -96.8657734856853$$
$$x_{23} = -94.7713783832921$$
$$x_{2} = -90.5825881785057$$
$$x_{43} = -88.4881930761125$$
$$x_{8} = -84.2994028713261$$
$$x_{24} = -82.2050077689329$$
$$x_{36} = -78.0162175641465$$
$$x_{1} = -75.9218224617533$$
$$x_{55} = -71.733032256967$$
$$x_{60} = -69.6386371545737$$
$$x_{5} = -65.4498469497874$$
$$x_{66} = -63.3554518473942$$
$$x_{53} = -59.1666616426078$$
$$x_{15} = -57.0722665402146$$
$$x_{25} = -52.8834763354282$$
$$x_{45} = -50.789081233035$$
$$x_{35} = -46.6002910282486$$
$$x_{21} = -44.5058959258554$$
$$x_{16} = -40.317105721069$$
$$x_{7} = -38.2227106186758$$
$$x_{11} = -34.0339204138894$$
$$x_{69} = -31.9395253114962$$
$$x_{64} = -27.7507351067098$$
$$x_{26} = -25.6563400043166$$
$$x_{14} = -21.4675497995303$$
$$x_{59} = -19.3731546971371$$
$$x_{6} = -15.1843644923507$$
$$x_{56} = -13.0899693899575$$
$$x_{44} = -8.90117918517108$$
$$x_{27} = -6.80678408277789$$
$$x_{18} = -2.61799387799149$$
$$x_{20} = -0.523598775598299$$
$$x_{62} = 3.66519142918809$$
$$x_{70} = 5.75958653158129$$
$$x_{10} = 9.94837673636768$$
$$x_{38} = 12.0427718387609$$
$$x_{29} = 16.2315620435473$$
$$x_{19} = 18.3259571459405$$
$$x_{37} = 22.5147473507269$$
$$x_{40} = 24.60914245312$$
$$x_{50} = 28.7979326579064$$
$$x_{3} = 30.8923277602996$$
$$x_{17} = 35.081117965086$$
$$x_{34} = 37.1755130674792$$
$$x_{30} = 41.3643032722656$$
$$x_{49} = 43.4586983746588$$
$$x_{39} = 47.6474885794452$$
$$x_{47} = 49.7418836818384$$
$$x_{22} = 53.9306738866248$$
$$x_{67} = 56.025068989018$$
$$x_{48} = 60.2138591938044$$
$$x_{51} = 62.3082542961976$$
$$x_{13} = 66.497044500984$$
$$x_{54} = 68.5914396033772$$
$$x_{46} = 72.7802298081635$$
$$x_{33} = 74.8746249105567$$
$$x_{31} = 79.0634151153431$$
$$x_{65} = 81.1578102177363$$
$$x_{71} = 85.3466004225227$$
$$x_{68} = 87.4409955249159$$
$$x_{42} = 91.6297857297023$$
$$x_{61} = 93.7241808320955$$
$$x_{63} = 97.9129710368819$$
$$x_{57} = 100.007366139275$$
$$x_{12} = 110.479341651241$$
$$x_{41} = 112.573736753634$$
$$x_{58} = 791.15774992903$$
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
$$x_{0} \leq x_{9}$$
Consideremos, por ejemplo, el punto
$$x_{0} = x_{9} - \frac{1}{10}$$
=
$$-45867.7763411866 + - \frac{1}{10}$$
=
$$-45867.8763411866$$
lo sustituimos en la expresión
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} \leq -2$$
$$5 \sin{\left(-45867.8763411866 \right)} + \cos{\left(\left(-45867.8763411866\right) 2 \right)} \leq -2$$
-2.60182118651354 <= -2

significa que una de las soluciones de nuestra ecuación será con:
$$x \leq -45867.7763411866$$
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Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
$$x \leq -45867.7763411866$$
$$x \geq -643.502895210309 \wedge x \leq -239.284640448423$$
$$x \geq -101.054563690472 \wedge x \leq -96.8657734856853$$
$$x \geq -94.7713783832921 \wedge x \leq -90.5825881785057$$
$$x \geq -88.4881930761125 \wedge x \leq -84.2994028713261$$
$$x \geq -82.2050077689329 \wedge x \leq -78.0162175641465$$
$$x \geq -75.9218224617533 \wedge x \leq -71.733032256967$$
$$x \geq -69.6386371545737 \wedge x \leq -65.4498469497874$$
$$x \geq -63.3554518473942 \wedge x \leq -59.1666616426078$$
$$x \geq -57.0722665402146 \wedge x \leq -52.8834763354282$$
$$x \geq -50.789081233035 \wedge x \leq -46.6002910282486$$
$$x \geq -44.5058959258554 \wedge x \leq -40.317105721069$$
$$x \geq -38.2227106186758 \wedge x \leq -34.0339204138894$$
$$x \geq -31.9395253114962 \wedge x \leq -27.7507351067098$$
$$x \geq -25.6563400043166 \wedge x \leq -21.4675497995303$$
$$x \geq -19.3731546971371 \wedge x \leq -15.1843644923507$$
$$x \geq -13.0899693899575 \wedge x \leq -8.90117918517108$$
$$x \geq -6.80678408277789 \wedge x \leq -2.61799387799149$$
$$x \geq -0.523598775598299 \wedge x \leq 3.66519142918809$$
$$x \geq 5.75958653158129 \wedge x \leq 9.94837673636768$$
$$x \geq 12.0427718387609 \wedge x \leq 16.2315620435473$$
$$x \geq 18.3259571459405 \wedge x \leq 22.5147473507269$$
$$x \geq 24.60914245312 \wedge x \leq 28.7979326579064$$
$$x \geq 30.8923277602996 \wedge x \leq 35.081117965086$$
$$x \geq 37.1755130674792 \wedge x \leq 41.3643032722656$$
$$x \geq 43.4586983746588 \wedge x \leq 47.6474885794452$$
$$x \geq 49.7418836818384 \wedge x \leq 53.9306738866248$$
$$x \geq 56.025068989018 \wedge x \leq 60.2138591938044$$
$$x \geq 62.3082542961976 \wedge x \leq 66.497044500984$$
$$x \geq 68.5914396033772 \wedge x \leq 72.7802298081635$$
$$x \geq 74.8746249105567 \wedge x \leq 79.0634151153431$$
$$x \geq 81.1578102177363 \wedge x \leq 85.3466004225227$$
$$x \geq 87.4409955249159 \wedge x \leq 91.6297857297023$$
$$x \geq 93.7241808320955 \wedge x \leq 97.9129710368819$$
$$x \geq 100.007366139275 \wedge x \leq 110.479341651241$$
$$x \geq 112.573736753634 \wedge x \leq 791.15774992903$$
Solución de la desigualdad en el gráfico
Respuesta rápida [src]
   /7*pi            11*pi\
And|---- <= x, x <= -----|
   \ 6                6  /
$$\frac{7 \pi}{6} \leq x \wedge x \leq \frac{11 \pi}{6}$$
(7*pi/6 <= x)∧(x <= 11*pi/6)
Respuesta rápida 2 [src]
 7*pi  11*pi 
[----, -----]
  6      6   
$$x\ in\ \left[\frac{7 \pi}{6}, \frac{11 \pi}{6}\right]$$
x in Interval(7*pi/6, 11*pi/6)