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cos^2(2x)+cos^2(4x)=1+ctg(6x) equation

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Numerical solution:

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The solution

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   2           2                    
cos (2*x) + cos (4*x) = 1 + cot(6*x)
$$\cos^{2}{\left(2 x \right)} + \cos^{2}{\left(4 x \right)} = \cot{\left(6 x \right)} + 1$$
The graph
Rapid solution [src]
     -11*pi
x1 = ------
       12  
$$x_{1} = - \frac{11 \pi}{12}$$
     -3*pi
x2 = -----
       4  
$$x_{2} = - \frac{3 \pi}{4}$$
     -7*pi
x3 = -----
       12 
$$x_{3} = - \frac{7 \pi}{12}$$
     -5*pi
x4 = -----
       12 
$$x_{4} = - \frac{5 \pi}{12}$$
     -pi 
x5 = ----
      4  
$$x_{5} = - \frac{\pi}{4}$$
     -pi 
x6 = ----
      12 
$$x_{6} = - \frac{\pi}{12}$$
     pi
x7 = --
     12
$$x_{7} = \frac{\pi}{12}$$
     pi
x8 = --
     4 
$$x_{8} = \frac{\pi}{4}$$
     5*pi
x9 = ----
      12 
$$x_{9} = \frac{5 \pi}{12}$$
      7*pi
x10 = ----
       12 
$$x_{10} = \frac{7 \pi}{12}$$
      3*pi
x11 = ----
       4  
$$x_{11} = \frac{3 \pi}{4}$$
      11*pi
x12 = -----
        12 
$$x_{12} = \frac{11 \pi}{12}$$
x12 = 11*pi/12
Sum and product of roots [src]
sum
  11*pi   3*pi   7*pi   5*pi   pi   pi   pi   pi   5*pi   7*pi   3*pi   11*pi
- ----- - ---- - ---- - ---- - -- - -- + -- + -- + ---- + ---- + ---- + -----
    12     4      12     12    4    12   12   4     12     12     4       12 
$$\left(\left(\left(\left(\left(\left(\left(\left(\left(\left(- \frac{11 \pi}{12} - \frac{3 \pi}{4}\right) - \frac{7 \pi}{12}\right) - \frac{5 \pi}{12}\right) - \frac{\pi}{4}\right) - \frac{\pi}{12}\right) + \frac{\pi}{12}\right) + \frac{\pi}{4}\right) + \frac{5 \pi}{12}\right) + \frac{7 \pi}{12}\right) + \frac{3 \pi}{4}\right) + \frac{11 \pi}{12}$$
=
0
$$0$$
product
-11*pi -3*pi -7*pi -5*pi -pi  -pi  pi pi 5*pi 7*pi 3*pi 11*pi
------*-----*-----*-----*----*----*--*--*----*----*----*-----
  12     4     12    12   4    12  12 4   12   12   4     12 
$$\frac{11 \pi}{12} \frac{3 \pi}{4} \frac{7 \pi}{12} \frac{5 \pi}{12} \frac{\pi}{4} \frac{\pi}{12} \cdot - \frac{\pi}{12} \cdot - \frac{\pi}{4} \cdot - \frac{5 \pi}{12} \cdot - \frac{7 \pi}{12} \cdot - \frac{11 \pi}{12} \left(- \frac{3 \pi}{4}\right)$$
=
         12
148225*pi  
-----------
12230590464
$$\frac{148225 \pi^{12}}{12230590464}$$
148225*pi^12/12230590464
Numerical answer [src]
x1 = 10.2101761241668
x2 = 50.0036830696375
x3 = -79.8488132787406
x4 = -67.8060414399797
x5 = 96.0803753222878
x6 = 68.329640215578
x7 = -91.8915851175014
x8 = 3.92699081698724
x9 = 78.2780169519457
x10 = -3.92699081698724
x11 = 80.3724120543389
x12 = 74.0892267471593
x13 = -87.7027949127151
x14 = -11.7809724509617
x15 = -9.68657734856853
x16 = 12.30457122656
x17 = -73.565627971561
x18 = -15.9697626557481
x19 = 69.9004365423729
x20 = 98.174770424681
x21 = -25.9181393921158
x22 = -7.59218224617533
x23 = 8.11578102177363
x24 = -43.720497762458
x25 = -1.83259571459405
x26 = 86.1319985859202
x27 = -33.7721210260903
x28 = -71.9948316447661
x29 = 14.3989663289532
x30 = -57.857664703612
x31 = -18.0641577581413
x32 = -96.0803753222878
x33 = -75.6600230739542
x34 = -81.9432083811338
x35 = -51.5744793964324
x36 = -69.9004365423729
x37 = 6.02138591938044
x38 = 2.35619449019234
x39 = -19.6349540849362
x40 = -45.8148928648512
x41 = 24.3473430653209
x42 = -97.6511716490827
x43 = 88.2263936883134
x44 = -85.6083998103219
x45 = -6.02138591938044
x46 = -77.7544181763474
x47 = 71.9948316447661
x48 = 90.3207887907066
x49 = 30.1069295969022
x50 = -35.8665161284835
x51 = 40.0553063332699
x52 = 58.3812634792103
x53 = 44.2440965380563
x54 = 20.1585528605345
x55 = -37.9609112308767
x56 = 59.9520598060052
x57 = 56.2868683768171
x58 = -62.0464549083984
x59 = -59.9520598060052
x60 = 84.037603483527
x61 = -63.6172512351933
x62 = 54.1924732744239
x63 = 37.9609112308767
x64 = -99.7455667514759
x65 = 42.1497014356631
x66 = 46.3384916404494
x67 = -13.8753675533549
x68 = -31.6777259236971
x69 = -41.6261026600648
x70 = 64.1408500107916
x71 = -93.9859802198946
x72 = 47.9092879672443
x73 = 18.0641577581413
x74 = -55.7632696012188
x75 = 52.0980781720307
x76 = -47.9092879672443
x77 = -53.6688744988256
x78 = 100.269165527074
x79 = 93.9859802198946
x80 = -50.0036830696375
x81 = 62.0464549083984
x82 = 15.9697626557481
x83 = 32.2013246992954
x84 = -29.5833308213039
x85 = -89.7971900151083
x86 = 66.2352451131848
x87 = 36.3901149040818
x88 = -84.037603483527
x89 = 22.2529479629277
x90 = -23.8237442897226
x91 = 76.1836218495525
x92 = 28.012534494509
x93 = -21.7293491873294
x94 = 25.9181393921158
x95 = -40.0553063332699
x96 = 34.2957198016886
x97 = 81.9432083811338
x98 = -28.012534494509
x99 = -65.7116463375865
x100 = 91.8915851175014
x100 = 91.8915851175014