Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$3 \sin{\left(3 x \right)} = 0$$
Solve this equationThe points of intersection with the axis X:
Analytical solution$$x_{1} = 0$$
$$x_{2} = \frac{\pi}{3}$$
Numerical solution$$x_{1} = 78.5398163397448$$
$$x_{2} = -77.4926187885482$$
$$x_{3} = -70.162235930172$$
$$x_{4} = 70.162235930172$$
$$x_{5} = 10.471975511966$$
$$x_{6} = -33.5103216382911$$
$$x_{7} = -43.9822971502571$$
$$x_{8} = -41.8879020478639$$
$$x_{9} = -94.2477796076938$$
$$x_{10} = 8.37758040957278$$
$$x_{11} = -26.1799387799149$$
$$x_{12} = 59.6902604182061$$
$$x_{13} = -90.0589894029074$$
$$x_{14} = 96.342174710087$$
$$x_{15} = 746.651854003174$$
$$x_{16} = 19.8967534727354$$
$$x_{17} = 94.2477796076938$$
$$x_{18} = 83.7758040957278$$
$$x_{19} = 50.2654824574367$$
$$x_{20} = 15.707963267949$$
$$x_{21} = -4.18879020478639$$
$$x_{22} = 63.8790506229925$$
$$x_{23} = -57.5958653158129$$
$$x_{24} = -17.8023583703422$$
$$x_{25} = 24.0855436775217$$
$$x_{26} = -55.5014702134197$$
$$x_{27} = -83.7758040957278$$
$$x_{28} = -99.4837673636768$$
$$x_{29} = 65.9734457253857$$
$$x_{30} = 61.7846555205993$$
$$x_{31} = 80.634211442138$$
$$x_{32} = 81.6814089933346$$
$$x_{33} = 109.955742875643$$
$$x_{34} = 39.7935069454707$$
$$x_{35} = 2491.28297429671$$
$$x_{36} = -54.4542726622231$$
$$x_{37} = 4.18879020478639$$
$$x_{38} = -24.0855436775217$$
$$x_{39} = 32.4631240870945$$
$$x_{40} = -15.707963267949$$
$$x_{41} = -2.0943951023932$$
$$x_{42} = -8.37758040957278$$
$$x_{43} = -68.0678408277789$$
$$x_{44} = 74.3510261349584$$
$$x_{45} = 54.4542726622231$$
$$x_{46} = 68.0678408277789$$
$$x_{47} = -81.6814089933346$$
$$x_{48} = -21.9911485751286$$
$$x_{49} = -50.2654824574367$$
$$x_{50} = 87.9645943005142$$
$$x_{51} = 76.4454212373516$$
$$x_{52} = -28.2743338823081$$
$$x_{53} = 41.8879020478639$$
$$x_{54} = 98.4365698124802$$
$$x_{55} = -19.8967534727354$$
$$x_{56} = -46.0766922526503$$
$$x_{57} = 37.6991118430775$$
$$x_{58} = -85.870199198121$$
$$x_{59} = -13.6135681655558$$
$$x_{60} = 30.3687289847013$$
$$x_{61} = -37.6991118430775$$
$$x_{62} = -87.9645943005142$$
$$x_{63} = 92.1533845053006$$
$$x_{64} = 72.2566310325652$$
$$x_{65} = 85.870199198121$$
$$x_{66} = 690.103186238558$$
$$x_{67} = 6.28318530717959$$
$$x_{68} = -31.4159265358979$$
$$x_{69} = 46.0766922526503$$
$$x_{70} = 21.9911485751286$$
$$x_{71} = 34.5575191894877$$
$$x_{72} = -63.8790506229925$$
$$x_{73} = -98.4365698124802$$
$$x_{74} = -79.5870138909414$$
$$x_{75} = -61.7846555205993$$
$$x_{76} = -35.6047167406843$$
$$x_{77} = -29.3215314335047$$
$$x_{78} = -39.7935069454707$$
$$x_{79} = 43.9822971502571$$
$$x_{80} = 52.3598775598299$$
$$x_{81} = -92.1533845053006$$
$$x_{82} = -10.471975511966$$
$$x_{83} = 26.1799387799149$$
$$x_{84} = 56.5486677646163$$
$$x_{85} = -11.5191730631626$$
$$x_{86} = 90.0589894029074$$
$$x_{87} = 28.2743338823081$$
$$x_{88} = -48.1710873550435$$
$$x_{89} = -72.2566310325652$$
$$x_{90} = 100.530964914873$$
$$x_{91} = 0$$
$$x_{92} = 2.0943951023932$$
$$x_{93} = -59.6902604182061$$
$$x_{94} = 17.8023583703422$$
$$x_{95} = 48.1710873550435$$
$$x_{96} = -65.9734457253857$$
$$x_{97} = -6.28318530717959$$