Given the inequality:
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} \geq -2$$
To solve this inequality, we must first solve the corresponding equation:
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} = -2$$
Solve:
Given the equation
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} = -2$$
transform
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} + 2 = 0$$
$$- 2 \sin^{2}{\left(x \right)} + 5 \sin{\left(x \right)} + 3 = 0$$
Do replacement
$$w = \sin{\left(x \right)}$$
This equation is of the form
a*w^2 + b*w + c = 0
A quadratic equation can be solved
using the discriminant.
The roots of the quadratic equation:
$$w_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$w_{2} = \frac{- \sqrt{D} - b}{2 a}$$
where D = b^2 - 4*a*c - it is the discriminant.
Because
$$a = -2$$
$$b = 5$$
$$c = 3$$
, then
D = b^2 - 4 * a * c =
(5)^2 - 4 * (-2) * (3) = 49
Because D > 0, then the equation has two roots.
w1 = (-b + sqrt(D)) / (2*a)
w2 = (-b - sqrt(D)) / (2*a)
or
$$w_{1} = - \frac{1}{2}$$
$$w_{2} = 3$$
do backward replacement
$$\sin{\left(x \right)} = w$$
Given the equation
$$\sin{\left(x \right)} = w$$
- this is the simplest trigonometric equation
This equation is transformed to
$$x = 2 \pi n + \operatorname{asin}{\left(w \right)}$$
$$x = 2 \pi n - \operatorname{asin}{\left(w \right)} + \pi$$
Or
$$x = 2 \pi n + \operatorname{asin}{\left(w \right)}$$
$$x = 2 \pi n - \operatorname{asin}{\left(w \right)} + \pi$$
, where n - is a integer
substitute w:
$$x_{1} = 2 \pi n + \operatorname{asin}{\left(w_{1} \right)}$$
$$x_{1} = 2 \pi n + \operatorname{asin}{\left(- \frac{1}{2} \right)}$$
$$x_{1} = 2 \pi n - \frac{\pi}{6}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(w_{2} \right)}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(3 \right)}$$
$$x_{2} = 2 \pi n + \operatorname{asin}{\left(3 \right)}$$
$$x_{3} = 2 \pi n - \operatorname{asin}{\left(w_{1} \right)} + \pi$$
$$x_{3} = 2 \pi n - \operatorname{asin}{\left(- \frac{1}{2} \right)} + \pi$$
$$x_{3} = 2 \pi n + \frac{7 \pi}{6}$$
$$x_{4} = 2 \pi n - \operatorname{asin}{\left(w_{2} \right)} + \pi$$
$$x_{4} = 2 \pi n + \pi - \operatorname{asin}{\left(3 \right)}$$
$$x_{4} = 2 \pi n + \pi - \operatorname{asin}{\left(3 \right)}$$
$$x_{1} = -45867.7763411866$$
$$x_{2} = 60.2138591938044$$
$$x_{3} = -75.9218224617533$$
$$x_{4} = 30.8923277602996$$
$$x_{5} = -6.80678408277789$$
$$x_{6} = 43.4586983746588$$
$$x_{7} = 18.3259571459405$$
$$x_{8} = 93.7241808320955$$
$$x_{9} = -78.0162175641465$$
$$x_{10} = -8.90117918517108$$
$$x_{11} = -643.502895210309$$
$$x_{12} = -96.8657734856853$$
$$x_{13} = 91.6297857297023$$
$$x_{14} = 791.15774992903$$
$$x_{15} = 53.9306738866248$$
$$x_{16} = -19.3731546971371$$
$$x_{17} = -71.733032256967$$
$$x_{18} = -50.789081233035$$
$$x_{19} = -40.317105721069$$
$$x_{20} = 37.1755130674792$$
$$x_{21} = 41.3643032722656$$
$$x_{22} = -21.4675497995303$$
$$x_{23} = -31.9395253114962$$
$$x_{24} = 24.60914245312$$
$$x_{25} = 16.2315620435473$$
$$x_{26} = -239.284640448423$$
$$x_{27} = -82.2050077689329$$
$$x_{28} = 12.0427718387609$$
$$x_{29} = 74.8746249105567$$
$$x_{30} = -15.1843644923507$$
$$x_{31} = 72.7802298081635$$
$$x_{32} = 22.5147473507269$$
$$x_{33} = 79.0634151153431$$
$$x_{34} = -52.8834763354282$$
$$x_{35} = -46.6002910282486$$
$$x_{36} = -34.0339204138894$$
$$x_{37} = -59.1666616426078$$
$$x_{38} = -69.6386371545737$$
$$x_{39} = 3.66519142918809$$
$$x_{40} = -27.7507351067098$$
$$x_{41} = 35.081117965086$$
$$x_{42} = -65.4498469497874$$
$$x_{43} = 87.4409955249159$$
$$x_{44} = -38.2227106186758$$
$$x_{45} = 66.497044500984$$
$$x_{46} = -101.054563690472$$
$$x_{47} = 62.3082542961976$$
$$x_{48} = 100.007366139275$$
$$x_{49} = -13.0899693899575$$
$$x_{50} = 97.9129710368819$$
$$x_{51} = -90.5825881785057$$
$$x_{52} = 5.75958653158129$$
$$x_{53} = 49.7418836818384$$
$$x_{54} = 85.3466004225227$$
$$x_{55} = 9.94837673636768$$
$$x_{56} = -2.61799387799149$$
$$x_{57} = 28.7979326579064$$
$$x_{58} = 68.5914396033772$$
$$x_{59} = 112.573736753634$$
$$x_{60} = -88.4881930761125$$
$$x_{61} = -25.6563400043166$$
$$x_{62} = -63.3554518473942$$
$$x_{63} = 110.479341651241$$
$$x_{64} = -94.7713783832921$$
$$x_{65} = 56.025068989018$$
$$x_{66} = -84.2994028713261$$
$$x_{67} = -44.5058959258554$$
$$x_{68} = -0.523598775598299$$
$$x_{69} = 47.6474885794452$$
$$x_{70} = 81.1578102177363$$
$$x_{71} = -57.0722665402146$$
$$x_{1} = -45867.7763411866$$
$$x_{2} = 60.2138591938044$$
$$x_{3} = -75.9218224617533$$
$$x_{4} = 30.8923277602996$$
$$x_{5} = -6.80678408277789$$
$$x_{6} = 43.4586983746588$$
$$x_{7} = 18.3259571459405$$
$$x_{8} = 93.7241808320955$$
$$x_{9} = -78.0162175641465$$
$$x_{10} = -8.90117918517108$$
$$x_{11} = -643.502895210309$$
$$x_{12} = -96.8657734856853$$
$$x_{13} = 91.6297857297023$$
$$x_{14} = 791.15774992903$$
$$x_{15} = 53.9306738866248$$
$$x_{16} = -19.3731546971371$$
$$x_{17} = -71.733032256967$$
$$x_{18} = -50.789081233035$$
$$x_{19} = -40.317105721069$$
$$x_{20} = 37.1755130674792$$
$$x_{21} = 41.3643032722656$$
$$x_{22} = -21.4675497995303$$
$$x_{23} = -31.9395253114962$$
$$x_{24} = 24.60914245312$$
$$x_{25} = 16.2315620435473$$
$$x_{26} = -239.284640448423$$
$$x_{27} = -82.2050077689329$$
$$x_{28} = 12.0427718387609$$
$$x_{29} = 74.8746249105567$$
$$x_{30} = -15.1843644923507$$
$$x_{31} = 72.7802298081635$$
$$x_{32} = 22.5147473507269$$
$$x_{33} = 79.0634151153431$$
$$x_{34} = -52.8834763354282$$
$$x_{35} = -46.6002910282486$$
$$x_{36} = -34.0339204138894$$
$$x_{37} = -59.1666616426078$$
$$x_{38} = -69.6386371545737$$
$$x_{39} = 3.66519142918809$$
$$x_{40} = -27.7507351067098$$
$$x_{41} = 35.081117965086$$
$$x_{42} = -65.4498469497874$$
$$x_{43} = 87.4409955249159$$
$$x_{44} = -38.2227106186758$$
$$x_{45} = 66.497044500984$$
$$x_{46} = -101.054563690472$$
$$x_{47} = 62.3082542961976$$
$$x_{48} = 100.007366139275$$
$$x_{49} = -13.0899693899575$$
$$x_{50} = 97.9129710368819$$
$$x_{51} = -90.5825881785057$$
$$x_{52} = 5.75958653158129$$
$$x_{53} = 49.7418836818384$$
$$x_{54} = 85.3466004225227$$
$$x_{55} = 9.94837673636768$$
$$x_{56} = -2.61799387799149$$
$$x_{57} = 28.7979326579064$$
$$x_{58} = 68.5914396033772$$
$$x_{59} = 112.573736753634$$
$$x_{60} = -88.4881930761125$$
$$x_{61} = -25.6563400043166$$
$$x_{62} = -63.3554518473942$$
$$x_{63} = 110.479341651241$$
$$x_{64} = -94.7713783832921$$
$$x_{65} = 56.025068989018$$
$$x_{66} = -84.2994028713261$$
$$x_{67} = -44.5058959258554$$
$$x_{68} = -0.523598775598299$$
$$x_{69} = 47.6474885794452$$
$$x_{70} = 81.1578102177363$$
$$x_{71} = -57.0722665402146$$
This roots
$$x_{1} = -45867.7763411866$$
$$x_{11} = -643.502895210309$$
$$x_{26} = -239.284640448423$$
$$x_{46} = -101.054563690472$$
$$x_{12} = -96.8657734856853$$
$$x_{64} = -94.7713783832921$$
$$x_{51} = -90.5825881785057$$
$$x_{60} = -88.4881930761125$$
$$x_{66} = -84.2994028713261$$
$$x_{27} = -82.2050077689329$$
$$x_{9} = -78.0162175641465$$
$$x_{3} = -75.9218224617533$$
$$x_{17} = -71.733032256967$$
$$x_{38} = -69.6386371545737$$
$$x_{42} = -65.4498469497874$$
$$x_{62} = -63.3554518473942$$
$$x_{37} = -59.1666616426078$$
$$x_{71} = -57.0722665402146$$
$$x_{34} = -52.8834763354282$$
$$x_{18} = -50.789081233035$$
$$x_{35} = -46.6002910282486$$
$$x_{67} = -44.5058959258554$$
$$x_{19} = -40.317105721069$$
$$x_{44} = -38.2227106186758$$
$$x_{36} = -34.0339204138894$$
$$x_{23} = -31.9395253114962$$
$$x_{40} = -27.7507351067098$$
$$x_{61} = -25.6563400043166$$
$$x_{22} = -21.4675497995303$$
$$x_{16} = -19.3731546971371$$
$$x_{30} = -15.1843644923507$$
$$x_{49} = -13.0899693899575$$
$$x_{10} = -8.90117918517108$$
$$x_{5} = -6.80678408277789$$
$$x_{56} = -2.61799387799149$$
$$x_{68} = -0.523598775598299$$
$$x_{39} = 3.66519142918809$$
$$x_{52} = 5.75958653158129$$
$$x_{55} = 9.94837673636768$$
$$x_{28} = 12.0427718387609$$
$$x_{25} = 16.2315620435473$$
$$x_{7} = 18.3259571459405$$
$$x_{32} = 22.5147473507269$$
$$x_{24} = 24.60914245312$$
$$x_{57} = 28.7979326579064$$
$$x_{4} = 30.8923277602996$$
$$x_{41} = 35.081117965086$$
$$x_{20} = 37.1755130674792$$
$$x_{21} = 41.3643032722656$$
$$x_{6} = 43.4586983746588$$
$$x_{69} = 47.6474885794452$$
$$x_{53} = 49.7418836818384$$
$$x_{15} = 53.9306738866248$$
$$x_{65} = 56.025068989018$$
$$x_{2} = 60.2138591938044$$
$$x_{47} = 62.3082542961976$$
$$x_{45} = 66.497044500984$$
$$x_{58} = 68.5914396033772$$
$$x_{31} = 72.7802298081635$$
$$x_{29} = 74.8746249105567$$
$$x_{33} = 79.0634151153431$$
$$x_{70} = 81.1578102177363$$
$$x_{54} = 85.3466004225227$$
$$x_{43} = 87.4409955249159$$
$$x_{13} = 91.6297857297023$$
$$x_{8} = 93.7241808320955$$
$$x_{50} = 97.9129710368819$$
$$x_{48} = 100.007366139275$$
$$x_{63} = 110.479341651241$$
$$x_{59} = 112.573736753634$$
$$x_{14} = 791.15774992903$$
is the points with change the sign of the inequality expression.
First define with the sign to the leftmost point:
$$x_{0} \leq x_{1}$$
For example, let's take the point
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$-45867.7763411866 + - \frac{1}{10}$$
=
$$-45867.8763411866$$
substitute to the expression
$$5 \sin{\left(x \right)} + \cos{\left(2 x \right)} \geq -2$$
$$5 \sin{\left(-45867.8763411866 \right)} + \cos{\left(\left(-45867.8763411866\right) 2 \right)} \geq -2$$
-2.60182118651354 >= -2
but
-2.60182118651354 < -2
Then
$$x \leq -45867.7763411866$$
no execute
one of the solutions of our inequality is:
$$x \geq -45867.7763411866 \wedge x \leq -643.502895210309$$
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x1 x11 x26 x46 x12 x64 x51 x60 x66 x27 x9 x3 x17 x38 x42 x62 x37 x71 x34 x18 x35 x67 x19 x44 x36 x23 x40 x61 x22 x16 x30 x49 x10 x5 x56 x68 x39 x52 x55 x28 x25 x7 x32 x24 x57 x4 x41 x20 x21 x6 x69 x53 x15 x65 x2 x47 x45 x58 x31 x29 x33 x70 x54 x43 x13 x8 x50 x48 x63 x59 x14Other solutions will get with the changeover to the next point
etc.
The answer:
$$x \geq -45867.7763411866 \wedge x \leq -643.502895210309$$
$$x \geq -239.284640448423 \wedge x \leq -101.054563690472$$
$$x \geq -96.8657734856853 \wedge x \leq -94.7713783832921$$
$$x \geq -90.5825881785057 \wedge x \leq -88.4881930761125$$
$$x \geq -84.2994028713261 \wedge x \leq -82.2050077689329$$
$$x \geq -78.0162175641465 \wedge x \leq -75.9218224617533$$
$$x \geq -71.733032256967 \wedge x \leq -69.6386371545737$$
$$x \geq -65.4498469497874 \wedge x \leq -63.3554518473942$$
$$x \geq -59.1666616426078 \wedge x \leq -57.0722665402146$$
$$x \geq -52.8834763354282 \wedge x \leq -50.789081233035$$
$$x \geq -46.6002910282486 \wedge x \leq -44.5058959258554$$
$$x \geq -40.317105721069 \wedge x \leq -38.2227106186758$$
$$x \geq -34.0339204138894 \wedge x \leq -31.9395253114962$$
$$x \geq -27.7507351067098 \wedge x \leq -25.6563400043166$$
$$x \geq -21.4675497995303 \wedge x \leq -19.3731546971371$$
$$x \geq -15.1843644923507 \wedge x \leq -13.0899693899575$$
$$x \geq -8.90117918517108 \wedge x \leq -6.80678408277789$$
$$x \geq -2.61799387799149 \wedge x \leq -0.523598775598299$$
$$x \geq 3.66519142918809 \wedge x \leq 5.75958653158129$$
$$x \geq 9.94837673636768 \wedge x \leq 12.0427718387609$$
$$x \geq 16.2315620435473 \wedge x \leq 18.3259571459405$$
$$x \geq 22.5147473507269 \wedge x \leq 24.60914245312$$
$$x \geq 28.7979326579064 \wedge x \leq 30.8923277602996$$
$$x \geq 35.081117965086 \wedge x \leq 37.1755130674792$$
$$x \geq 41.3643032722656 \wedge x \leq 43.4586983746588$$
$$x \geq 47.6474885794452 \wedge x \leq 49.7418836818384$$
$$x \geq 53.9306738866248 \wedge x \leq 56.025068989018$$
$$x \geq 60.2138591938044 \wedge x \leq 62.3082542961976$$
$$x \geq 66.497044500984 \wedge x \leq 68.5914396033772$$
$$x \geq 72.7802298081635 \wedge x \leq 74.8746249105567$$
$$x \geq 79.0634151153431 \wedge x \leq 81.1578102177363$$
$$x \geq 85.3466004225227 \wedge x \leq 87.4409955249159$$
$$x \geq 91.6297857297023 \wedge x \leq 93.7241808320955$$
$$x \geq 97.9129710368819 \wedge x \leq 100.007366139275$$
$$x \geq 110.479341651241 \wedge x \leq 112.573736753634$$
$$x \geq 791.15774992903$$