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tg^2×3x+tg3x>0. inequation

A inequation with variable

The solution

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   2                    
tan (3)*x + tan(3*x) > 0
$$x \tan^{2}{\left(3 \right)} + \tan{\left(3 x \right)} > 0$$
x*tan(3)^2 + tan(3*x) > 0
Detail solution
Given the inequality:
$$x \tan^{2}{\left(3 \right)} + \tan{\left(3 x \right)} > 0$$
To solve this inequality, we must first solve the corresponding equation:
$$x \tan^{2}{\left(3 \right)} + \tan{\left(3 x \right)} = 0$$
Solve:
Given the equation
$$x \tan^{2}{\left(3 \right)} + \tan{\left(3 x \right)} = 0$$
transform
$$x \tan^{2}{\left(3 \right)} + \tan{\left(3 x \right)} - 1 = 0$$
$$x \tan^{2}{\left(3 \right)} + \tan{\left(3 x \right)} - 1 = 0$$
Do replacement
$$w = \tan{\left(3 \right)}$$
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
$$a = x$$
$$b = 0$$
$$c = \tan{\left(3 x \right)} - 1$$
, then
D = b^2 - 4 * a * c = 

(0)^2 - 4 * (x) * (-1 + tan(3*x)) = -4*x*(-1 + tan(3*x))

The equation has two roots.
w1 = (-b + sqrt(D)) / (2*a)

w2 = (-b - sqrt(D)) / (2*a)

or
$$w_{1} = \frac{\sqrt{- x \left(\tan{\left(3 x \right)} - 1\right)}}{x}$$
$$w_{2} = - \frac{\sqrt{- x \left(\tan{\left(3 x \right)} - 1\right)}}{x}$$
do backward replacement
$$\tan{\left(3 \right)} = w$$
substitute w:
$$x_{1} = -11.4430206365735$$
$$x_{2} = -13.5241732976706$$
$$x_{3} = 41.6537716005031$$
$$x_{4} = 63.5750354548075$$
$$x_{5} = 36.4394644196323$$
$$x_{6} = 61.4860527734845$$
$$x_{7} = -23.93465682743$$
$$x_{8} = -77.1582771296535$$
$$x_{9} = 69.8432464067169$$
$$x_{10} = 43.7401037273121$$
$$x_{11} = 14.5648531214347$$
$$x_{12} = -99.1137933230801$$
$$x_{13} = 83.4298541758724$$
$$x_{14} = -75.0680562341485$$
$$x_{15} = 47.9137492552259$$
$$x_{16} = -19.7694282924916$$
$$x_{17} = 21.8518588464878$$
$$x_{18} = -4.1606760834944$$
$$x_{19} = -67.7536424860438$$
$$x_{20} = -17.6873507300709$$
$$x_{21} = 98.0680086959402$$
$$x_{22} = 28.1013912068659$$
$$x_{23} = 12.4835638214075$$
$$x_{24} = 74.0230073081604$$
$$x_{25} = 100.159601637212$$
$$x_{26} = 50.0010381242272$$
$$x_{27} = 71.9330377162168$$
$$x_{28} = -71.9330377162168$$
$$x_{29} = -91.793830738348$$
$$x_{30} = -7.28141976377463$$
$$x_{31} = 80.2939012171025$$
$$x_{32} = -6.24113746091876$$
$$x_{33} = -53.1325189107123$$
$$x_{34} = 54.1764855935747$$
$$x_{35} = 52.0886210692883$$
$$x_{36} = 19.7694282924916$$
$$x_{37} = 23.93465682743$$
$$x_{38} = 81.3391835252855$$
$$x_{39} = 37.4821465223781$$
$$x_{40} = 58.3530101922313$$
$$x_{41} = -31.2274529673745$$
$$x_{42} = -81.3391835252855$$
$$x_{43} = 10.4025393964027$$
$$x_{44} = -59.3972983233981$$
$$x_{45} = 95.9765127508869$$
$$x_{46} = -87.611596123346$$
$$x_{47} = -41.6537716005031$$
$$x_{48} = -47.9137492552259$$
$$x_{49} = -50.0010381242272$$
$$x_{50} = 15.605607050105$$
$$x_{51} = 76.1131465135857$$
$$x_{52} = -15.605607050105$$
$$x_{53} = -83.4298541758724$$
$$x_{54} = 56.2646193420575$$
$$x_{55} = 59.3972983233981$$
$$x_{56} = 26.01783227767$$
$$x_{57} = -21.8518588464878$$
$$x_{58} = -28.1013912068659$$
$$x_{59} = 34.3543772929176$$
$$x_{60} = -37.4821465223781$$
$$x_{61} = 32.2696658761755$$
$$x_{62} = -69.8432464067169$$
$$x_{63} = -95.9765127508869$$
$$x_{64} = -26.01783227767$$
$$x_{65} = -52.0886210692883$$
$$x_{66} = 2.08031316621878$$
$$x_{67} = -33.3119742070762$$
$$x_{68} = 8.32174397747159$$
$$x_{69} = 85.5206605372381$$
$$x_{70} = -35.3968743357863$$
$$x_{71} = -57.3087833759606$$
$$x_{72} = 0$$
$$x_{73} = -65.6642355039225$$
$$x_{74} = 65.6642355039225$$
$$x_{75} = 67.7536424860438$$
$$x_{76} = -93.8851184579335$$
$$x_{77} = 17.6873507300709$$
$$x_{78} = -55.220519578813$$
$$x_{79} = 4.1606760834944$$
$$x_{80} = -2.08031316621878$$
$$x_{81} = -45.8267669863934$$
$$x_{82} = -61.4860527734845$$
$$x_{83} = -9.36211547427728$$
$$x_{84} = 78.2034470915481$$
$$x_{85} = 87.611596123346$$
$$x_{86} = -63.5750354548075$$
$$x_{87} = -97.0222483139387$$
$$x_{88} = 39.5677822348798$$
$$x_{89} = 45.8267669863934$$
$$x_{90} = -89.7026547940409$$
$$x_{91} = -30.1853360040102$$
$$x_{92} = 6.24113746091876$$
$$x_{93} = -79.2486554340557$$
$$x_{94} = -85.5206605372381$$
$$x_{95} = 30.1853360040102$$
$$x_{96} = -74.0230073081604$$
$$x_{97} = -43.7401037273121$$
$$x_{98} = -39.5677822348798$$
$$x_{1} = -11.4430206365735$$
$$x_{2} = -13.5241732976706$$
$$x_{3} = 41.6537716005031$$
$$x_{4} = 63.5750354548075$$
$$x_{5} = 36.4394644196323$$
$$x_{6} = 61.4860527734845$$
$$x_{7} = -23.93465682743$$
$$x_{8} = -77.1582771296535$$
$$x_{9} = 69.8432464067169$$
$$x_{10} = 43.7401037273121$$
$$x_{11} = 14.5648531214347$$
$$x_{12} = -99.1137933230801$$
$$x_{13} = 83.4298541758724$$
$$x_{14} = -75.0680562341485$$
$$x_{15} = 47.9137492552259$$
$$x_{16} = -19.7694282924916$$
$$x_{17} = 21.8518588464878$$
$$x_{18} = -4.1606760834944$$
$$x_{19} = -67.7536424860438$$
$$x_{20} = -17.6873507300709$$
$$x_{21} = 98.0680086959402$$
$$x_{22} = 28.1013912068659$$
$$x_{23} = 12.4835638214075$$
$$x_{24} = 74.0230073081604$$
$$x_{25} = 100.159601637212$$
$$x_{26} = 50.0010381242272$$
$$x_{27} = 71.9330377162168$$
$$x_{28} = -71.9330377162168$$
$$x_{29} = -91.793830738348$$
$$x_{30} = -7.28141976377463$$
$$x_{31} = 80.2939012171025$$
$$x_{32} = -6.24113746091876$$
$$x_{33} = -53.1325189107123$$
$$x_{34} = 54.1764855935747$$
$$x_{35} = 52.0886210692883$$
$$x_{36} = 19.7694282924916$$
$$x_{37} = 23.93465682743$$
$$x_{38} = 81.3391835252855$$
$$x_{39} = 37.4821465223781$$
$$x_{40} = 58.3530101922313$$
$$x_{41} = -31.2274529673745$$
$$x_{42} = -81.3391835252855$$
$$x_{43} = 10.4025393964027$$
$$x_{44} = -59.3972983233981$$
$$x_{45} = 95.9765127508869$$
$$x_{46} = -87.611596123346$$
$$x_{47} = -41.6537716005031$$
$$x_{48} = -47.9137492552259$$
$$x_{49} = -50.0010381242272$$
$$x_{50} = 15.605607050105$$
$$x_{51} = 76.1131465135857$$
$$x_{52} = -15.605607050105$$
$$x_{53} = -83.4298541758724$$
$$x_{54} = 56.2646193420575$$
$$x_{55} = 59.3972983233981$$
$$x_{56} = 26.01783227767$$
$$x_{57} = -21.8518588464878$$
$$x_{58} = -28.1013912068659$$
$$x_{59} = 34.3543772929176$$
$$x_{60} = -37.4821465223781$$
$$x_{61} = 32.2696658761755$$
$$x_{62} = -69.8432464067169$$
$$x_{63} = -95.9765127508869$$
$$x_{64} = -26.01783227767$$
$$x_{65} = -52.0886210692883$$
$$x_{66} = 2.08031316621878$$
$$x_{67} = -33.3119742070762$$
$$x_{68} = 8.32174397747159$$
$$x_{69} = 85.5206605372381$$
$$x_{70} = -35.3968743357863$$
$$x_{71} = -57.3087833759606$$
$$x_{72} = 0$$
$$x_{73} = -65.6642355039225$$
$$x_{74} = 65.6642355039225$$
$$x_{75} = 67.7536424860438$$
$$x_{76} = -93.8851184579335$$
$$x_{77} = 17.6873507300709$$
$$x_{78} = -55.220519578813$$
$$x_{79} = 4.1606760834944$$
$$x_{80} = -2.08031316621878$$
$$x_{81} = -45.8267669863934$$
$$x_{82} = -61.4860527734845$$
$$x_{83} = -9.36211547427728$$
$$x_{84} = 78.2034470915481$$
$$x_{85} = 87.611596123346$$
$$x_{86} = -63.5750354548075$$
$$x_{87} = -97.0222483139387$$
$$x_{88} = 39.5677822348798$$
$$x_{89} = 45.8267669863934$$
$$x_{90} = -89.7026547940409$$
$$x_{91} = -30.1853360040102$$
$$x_{92} = 6.24113746091876$$
$$x_{93} = -79.2486554340557$$
$$x_{94} = -85.5206605372381$$
$$x_{95} = 30.1853360040102$$
$$x_{96} = -74.0230073081604$$
$$x_{97} = -43.7401037273121$$
$$x_{98} = -39.5677822348798$$
This roots
$$x_{12} = -99.1137933230801$$
$$x_{87} = -97.0222483139387$$
$$x_{63} = -95.9765127508869$$
$$x_{76} = -93.8851184579335$$
$$x_{29} = -91.793830738348$$
$$x_{90} = -89.7026547940409$$
$$x_{46} = -87.611596123346$$
$$x_{94} = -85.5206605372381$$
$$x_{53} = -83.4298541758724$$
$$x_{42} = -81.3391835252855$$
$$x_{93} = -79.2486554340557$$
$$x_{8} = -77.1582771296535$$
$$x_{14} = -75.0680562341485$$
$$x_{96} = -74.0230073081604$$
$$x_{28} = -71.9330377162168$$
$$x_{62} = -69.8432464067169$$
$$x_{19} = -67.7536424860438$$
$$x_{73} = -65.6642355039225$$
$$x_{86} = -63.5750354548075$$
$$x_{82} = -61.4860527734845$$
$$x_{44} = -59.3972983233981$$
$$x_{71} = -57.3087833759606$$
$$x_{78} = -55.220519578813$$
$$x_{33} = -53.1325189107123$$
$$x_{65} = -52.0886210692883$$
$$x_{49} = -50.0010381242272$$
$$x_{48} = -47.9137492552259$$
$$x_{81} = -45.8267669863934$$
$$x_{97} = -43.7401037273121$$
$$x_{47} = -41.6537716005031$$
$$x_{98} = -39.5677822348798$$
$$x_{60} = -37.4821465223781$$
$$x_{70} = -35.3968743357863$$
$$x_{67} = -33.3119742070762$$
$$x_{41} = -31.2274529673745$$
$$x_{91} = -30.1853360040102$$
$$x_{58} = -28.1013912068659$$
$$x_{64} = -26.01783227767$$
$$x_{7} = -23.93465682743$$
$$x_{57} = -21.8518588464878$$
$$x_{16} = -19.7694282924916$$
$$x_{20} = -17.6873507300709$$
$$x_{52} = -15.605607050105$$
$$x_{2} = -13.5241732976706$$
$$x_{1} = -11.4430206365735$$
$$x_{83} = -9.36211547427728$$
$$x_{30} = -7.28141976377463$$
$$x_{32} = -6.24113746091876$$
$$x_{18} = -4.1606760834944$$
$$x_{80} = -2.08031316621878$$
$$x_{72} = 0$$
$$x_{66} = 2.08031316621878$$
$$x_{79} = 4.1606760834944$$
$$x_{92} = 6.24113746091876$$
$$x_{68} = 8.32174397747159$$
$$x_{43} = 10.4025393964027$$
$$x_{23} = 12.4835638214075$$
$$x_{11} = 14.5648531214347$$
$$x_{50} = 15.605607050105$$
$$x_{77} = 17.6873507300709$$
$$x_{36} = 19.7694282924916$$
$$x_{17} = 21.8518588464878$$
$$x_{37} = 23.93465682743$$
$$x_{56} = 26.01783227767$$
$$x_{22} = 28.1013912068659$$
$$x_{95} = 30.1853360040102$$
$$x_{61} = 32.2696658761755$$
$$x_{59} = 34.3543772929176$$
$$x_{5} = 36.4394644196323$$
$$x_{39} = 37.4821465223781$$
$$x_{88} = 39.5677822348798$$
$$x_{3} = 41.6537716005031$$
$$x_{10} = 43.7401037273121$$
$$x_{89} = 45.8267669863934$$
$$x_{15} = 47.9137492552259$$
$$x_{26} = 50.0010381242272$$
$$x_{35} = 52.0886210692883$$
$$x_{34} = 54.1764855935747$$
$$x_{54} = 56.2646193420575$$
$$x_{40} = 58.3530101922313$$
$$x_{55} = 59.3972983233981$$
$$x_{6} = 61.4860527734845$$
$$x_{4} = 63.5750354548075$$
$$x_{74} = 65.6642355039225$$
$$x_{75} = 67.7536424860438$$
$$x_{9} = 69.8432464067169$$
$$x_{27} = 71.9330377162168$$
$$x_{24} = 74.0230073081604$$
$$x_{51} = 76.1131465135857$$
$$x_{84} = 78.2034470915481$$
$$x_{31} = 80.2939012171025$$
$$x_{38} = 81.3391835252855$$
$$x_{13} = 83.4298541758724$$
$$x_{69} = 85.5206605372381$$
$$x_{85} = 87.611596123346$$
$$x_{45} = 95.9765127508869$$
$$x_{21} = 98.0680086959402$$
$$x_{25} = 100.159601637212$$
is the points with change the sign of the inequality expression.
First define with the sign to the leftmost point:
$$x_{0} < x_{12}$$
For example, let's take the point
$$x_{0} = x_{12} - \frac{1}{10}$$
=
$$-99.1137933230801 + - \frac{1}{10}$$
=
$$-99.2137933230801$$
substitute to the expression
$$x \tan^{2}{\left(3 \right)} + \tan{\left(3 x \right)} > 0$$
$$\left(-99.2137933230801\right) \tan^{2}{\left(3 \right)} + \tan{\left(\left(-99.2137933230801\right) 3 \right)} > 0$$
                                       2       
1.05029134212031 - 99.2137933230801*tan (3) > 0
    

Then
$$x < -99.1137933230801$$
no execute
one of the solutions of our inequality is:
$$x > -99.1137933230801 \wedge x < -97.0222483139387$$
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       x12      x87      x63      x76      x29      x90      x46      x94      x53      x42      x93      x8      x14      x96      x28      x62      x19      x73      x86      x82      x44      x71      x78      x33      x65      x49      x48      x81      x97      x47      x98      x60      x70      x67      x41      x91      x58      x64      x7      x57      x16      x20      x52      x2      x1      x83      x30      x32      x18      x80      x72      x66      x79      x92      x68      x43      x23      x11      x50      x77      x36      x17      x37      x56      x22      x95      x61      x59      x5      x39      x88      x3      x10      x89      x15      x26      x35      x34      x54      x40      x55      x6      x4      x74      x75      x9      x27      x24      x51      x84      x31      x38      x13      x69      x85      x45      x21      x25

Other solutions will get with the changeover to the next point
etc.
The answer:
$$x > -99.1137933230801 \wedge x < -97.0222483139387$$
$$x > -95.9765127508869 \wedge x < -93.8851184579335$$
$$x > -91.793830738348 \wedge x < -89.7026547940409$$
$$x > -87.611596123346 \wedge x < -85.5206605372381$$
$$x > -83.4298541758724 \wedge x < -81.3391835252855$$
$$x > -79.2486554340557 \wedge x < -77.1582771296535$$
$$x > -75.0680562341485 \wedge x < -74.0230073081604$$
$$x > -71.9330377162168 \wedge x < -69.8432464067169$$
$$x > -67.7536424860438 \wedge x < -65.6642355039225$$
$$x > -63.5750354548075 \wedge x < -61.4860527734845$$
$$x > -59.3972983233981 \wedge x < -57.3087833759606$$
$$x > -55.220519578813 \wedge x < -53.1325189107123$$
$$x > -52.0886210692883 \wedge x < -50.0010381242272$$
$$x > -47.9137492552259 \wedge x < -45.8267669863934$$
$$x > -43.7401037273121 \wedge x < -41.6537716005031$$
$$x > -39.5677822348798 \wedge x < -37.4821465223781$$
$$x > -35.3968743357863 \wedge x < -33.3119742070762$$
$$x > -31.2274529673745 \wedge x < -30.1853360040102$$
$$x > -28.1013912068659 \wedge x < -26.01783227767$$
$$x > -23.93465682743 \wedge x < -21.8518588464878$$
$$x > -19.7694282924916 \wedge x < -17.6873507300709$$
$$x > -15.605607050105 \wedge x < -13.5241732976706$$
$$x > -11.4430206365735 \wedge x < -9.36211547427728$$
$$x > -7.28141976377463 \wedge x < -6.24113746091876$$
$$x > -4.1606760834944 \wedge x < -2.08031316621878$$
$$x > 0 \wedge x < 2.08031316621878$$
$$x > 4.1606760834944 \wedge x < 6.24113746091876$$
$$x > 8.32174397747159 \wedge x < 10.4025393964027$$
$$x > 12.4835638214075 \wedge x < 14.5648531214347$$
$$x > 15.605607050105 \wedge x < 17.6873507300709$$
$$x > 19.7694282924916 \wedge x < 21.8518588464878$$
$$x > 23.93465682743 \wedge x < 26.01783227767$$
$$x > 28.1013912068659 \wedge x < 30.1853360040102$$
$$x > 32.2696658761755 \wedge x < 34.3543772929176$$
$$x > 36.4394644196323 \wedge x < 37.4821465223781$$
$$x > 39.5677822348798 \wedge x < 41.6537716005031$$
$$x > 43.7401037273121 \wedge x < 45.8267669863934$$
$$x > 47.9137492552259 \wedge x < 50.0010381242272$$
$$x > 52.0886210692883 \wedge x < 54.1764855935747$$
$$x > 56.2646193420575 \wedge x < 58.3530101922313$$
$$x > 59.3972983233981 \wedge x < 61.4860527734845$$
$$x > 63.5750354548075 \wedge x < 65.6642355039225$$
$$x > 67.7536424860438 \wedge x < 69.8432464067169$$
$$x > 71.9330377162168 \wedge x < 74.0230073081604$$
$$x > 76.1131465135857 \wedge x < 78.2034470915481$$
$$x > 80.2939012171025 \wedge x < 81.3391835252855$$
$$x > 83.4298541758724 \wedge x < 85.5206605372381$$
$$x > 87.611596123346 \wedge x < 95.9765127508869$$
$$x > 98.0680086959402 \wedge x < 100.159601637212$$
Solving inequality on a graph