The teacher will be very surprised to see your correct solution 😉
2 2 cos (2*x) + cos (4*x) = 1 + cot(6*x)
-11*pi x1 = ------ 12
-3*pi x2 = ----- 4
-7*pi x3 = ----- 12
-5*pi x4 = ----- 12
-pi x5 = ---- 4
-pi x6 = ---- 12
pi x7 = -- 12
pi x8 = -- 4
5*pi x9 = ---- 12
7*pi x10 = ---- 12
3*pi x11 = ---- 4
11*pi x12 = ----- 12
x12 = 11*pi/12
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
=
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
=
12 148225*pi ----------- 12230590464
148225*pi^12/12230590464
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