Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$3 x - \sin{\left(3 x \right)} = 0$$
Solve this equationThe points of intersection with the axis X:
Numerical solution$$x_{1} = -3.07951875468401 \cdot 10^{-5}$$
$$x_{2} = 2.95687217929344 \cdot 10^{-5}$$
$$x_{3} = 2.61787477773479 \cdot 10^{-5}$$
$$x_{4} = 0$$
$$x_{5} = 3.79126422867833 \cdot 10^{-5}$$
$$x_{6} = -5.13310156383023 \cdot 10^{-5}$$
$$x_{7} = -3.23738620069361 \cdot 10^{-5}$$
$$x_{8} = 3.28552552703676 \cdot 10^{-5}$$
$$x_{9} = -3.03748031442664 \cdot 10^{-5}$$
$$x_{10} = -5.47644485231154 \cdot 10^{-5}$$
$$x_{11} = 6.22528921985556 \cdot 10^{-5}$$
$$x_{12} = 3.81011017140862 \cdot 10^{-5}$$
$$x_{13} = 1.24709933362099 \cdot 10^{-5}$$
$$x_{14} = -4.74515571467871 \cdot 10^{-5}$$
$$x_{15} = 3.13001463327587 \cdot 10^{-5}$$
$$x_{16} = 6.17590305891602 \cdot 10^{-5}$$
$$x_{17} = 4.0643060119909 \cdot 10^{-5}$$
$$x_{18} = 2.47732655975024 \cdot 10^{-5}$$
$$x_{19} = -1.01152050997057 \cdot 10^{-5}$$
$$x_{20} = -1.42711505764305 \cdot 10^{-5}$$
$$x_{21} = 4.18003078140491 \cdot 10^{-5}$$
$$x_{22} = -3.24047412993241 \cdot 10^{-5}$$
$$x_{23} = 2.0811409948095 \cdot 10^{-5}$$
$$x_{24} = -4.12447384928281 \cdot 10^{-5}$$
$$x_{25} = 4.79194478669838 \cdot 10^{-5}$$
$$x_{26} = 4.13315071829598 \cdot 10^{-5}$$
$$x_{27} = -1.93927311932185 \cdot 10^{-5}$$
$$x_{28} = -3.5335677405585 \cdot 10^{-5}$$
$$x_{29} = 5.40328293972531 \cdot 10^{-5}$$
$$x_{30} = 5.30137084514175 \cdot 10^{-5}$$
$$x_{31} = -3.4849465010032 \cdot 10^{-5}$$
$$x_{32} = -6.30286392960451 \cdot 10^{-5}$$