El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$- \sin{\left(x \right)} - 3 \sin{\left(3 x \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = 0$$
$$x_{2} = \pi$$
$$x_{3} = \frac{i \left(\log{\left(3 \right)} - \log{\left(-2 - \sqrt{5} i \right)}\right)}{2}$$
$$x_{4} = \frac{i \left(\log{\left(3 \right)} - \log{\left(-2 + \sqrt{5} i \right)}\right)}{2}$$
Solución numérica$$x_{1} = 12.5663706143592$$
$$x_{2} = -70.2653003704864$$
$$x_{3} = 32.5661885274089$$
$$x_{4} = 78.5398163397448$$
$$x_{5} = -41.9909664881782$$
$$x_{6} = 92.2564489456149$$
$$x_{7} = -65.9734457253857$$
$$x_{8} = 52.2568131195156$$
$$x_{9} = -61.6815910802849$$
$$x_{10} = -15.707963267949$$
$$x_{11} = 54.5573371025374$$
$$x_{12} = 50.2654824574367$$
$$x_{13} = 81.6814089933346$$
$$x_{14} = -33.4072571979768$$
$$x_{15} = -32.5661885274089$$
$$x_{16} = -48.2741517953578$$
$$x_{17} = -96.2391102697727$$
$$x_{18} = -89.9559249625931$$
$$x_{19} = -56.5486677646163$$
$$x_{20} = -51.4157444489476$$
$$x_{21} = -83.6727396554135$$
$$x_{22} = -75.398223686155$$
$$x_{23} = -98.5396342527945$$
$$x_{24} = 89.9559249625931$$
$$x_{25} = 56.5486677646163$$
$$x_{26} = -79.6900783312558$$
$$x_{27} = 96.2391102697727$$
$$x_{28} = 45.973627812336$$
$$x_{29} = 15.707963267949$$
$$x_{30} = 1.99133066207886$$
$$x_{31} = -59.6902604182061$$
$$x_{32} = 21.9911485751286$$
$$x_{33} = 6.28318530717959$$
$$x_{34} = -17.6992939300278$$
$$x_{35} = 23.9824792372074$$
$$x_{36} = -87.9645943005142$$
$$x_{37} = 26.2830032202293$$
$$x_{38} = -28.2743338823081$$
$$x_{39} = 10.5750399522803$$
$$x_{40} = 63.9821150633068$$
$$x_{41} = -9.42477796076938$$
$$x_{42} = 8.27451596925845$$
$$x_{43} = 59.6902604182061$$
$$x_{44} = -23.9824792372074$$
$$x_{45} = -67.9647763874645$$
$$x_{46} = 28.2743338823081$$
$$x_{47} = 94.2477796076938$$
$$x_{48} = -72.2566310325652$$
$$x_{49} = -74.2479616946441$$
$$x_{50} = 37.6991118430775$$
$$x_{51} = -50.2654824574367$$
$$x_{52} = -94.2477796076938$$
$$x_{53} = -10.5750399522803$$
$$x_{54} = 85.9732636384354$$
$$x_{55} = 70.2653003704864$$
$$x_{56} = 115.088666191311$$
$$x_{57} = 4.29185464510072$$
$$x_{58} = 83.6727396554135$$
$$x_{59} = -4.29185464510072$$
$$x_{60} = -37.6991118430775$$
$$x_{61} = 19.9998179130497$$
$$x_{62} = -45.973627812336$$
$$x_{63} = -1.99133066207886$$
$$x_{64} = -13.7166326058701$$
$$x_{65} = 48.2741517953578$$
$$x_{66} = 76.548485677666$$
$$x_{67} = -81.6814089933346$$
$$x_{68} = 43.9822971502571$$
$$x_{69} = 98.5396342527945$$
$$x_{70} = -19.9998179130497$$
$$x_{71} = 61.6815910802849$$
$$x_{72} = -26.2830032202293$$
$$x_{73} = -57.6989297561272$$
$$x_{74} = 0$$
$$x_{75} = -21.9911485751286$$
$$x_{76} = 30.265664544387$$
$$x_{77} = -63.9821150633068$$
$$x_{78} = 100.530964914873$$
$$x_{79} = 34.5575191894877$$
$$x_{80} = 65.9734457253857$$
$$x_{81} = 113.097335529233$$
$$x_{82} = 17.6992939300278$$
$$x_{83} = -35.7077811809987$$
$$x_{84} = 74.2479616946441$$
$$x_{85} = -6.28318530717959$$
$$x_{86} = 67.9647763874645$$
$$x_{87} = -85.9732636384354$$
$$x_{88} = 39.6904425051564$$
$$x_{89} = -39.6904425051564$$
$$x_{90} = -11.4161086228482$$
$$x_{91} = -43.9822971502571$$
$$x_{92} = -92.2564489456149$$
$$x_{93} = 72.2566310325652$$
$$x_{94} = 41.9909664881782$$
$$x_{95} = 87.9645943005142$$