Hallemos los puntos de flexiones, para eso hay que resolver la ecuación
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(la segunda derivada es igual a cero),
las raíces de la ecuación obtenida serán los puntos de flexión para el gráfico de la función indicado:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
segunda derivada$$i \left(\frac{9 \sin^{2}{\left(\frac{x}{2} \right)} \sin^{2}{\left(3 x \right)} \operatorname{sign}{\left(\cos{\left(3 x \right)} \right)}}{\cos{\left(3 x \right)}} - \frac{9 \sin^{2}{\left(\frac{x}{2} \right)} \sin^{2}{\left(3 x \right)} \left|{\cos{\left(3 x \right)}}\right|}{\cos^{2}{\left(3 x \right)}} - \frac{19 \sin^{2}{\left(\frac{x}{2} \right)} \left|{\cos{\left(3 x \right)}}\right|}{2} - 3 \sin{\left(\frac{x}{2} \right)} \sin{\left(3 x \right)} \cos{\left(\frac{x}{2} \right)} \operatorname{sign}{\left(\cos{\left(3 x \right)} \right)} - \frac{3 \sin{\left(\frac{x}{2} \right)} \sin{\left(3 x \right)} \cos{\left(\frac{x}{2} \right)} \left|{\cos{\left(3 x \right)}}\right|}{\cos{\left(3 x \right)}} + \frac{\cos^{2}{\left(\frac{x}{2} \right)} \left|{\cos{\left(3 x \right)}}\right|}{2}\right) = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 17.9734625556164$$
$$x_{2} = -12.7650465573008$$
$$x_{3} = 37.8977877860192$$
$$x_{4} = 0.198675942941671$$
$$x_{5} = -24.256647862796$$
$$x_{6} = -55.672574398694$$
$$x_{7} = -87.7659183575725$$
$$x_{8} = -60.1633453220313$$
$$x_{9} = -89.7040076030613$$
$$x_{10} = -69.9911317448978$$
$$x_{11} = -95.9871929102409$$
$$x_{12} = -99.654871548951$$
$$x_{13} = 37.5004359001358$$
$$x_{14} = -79.9419956907876$$
$$x_{15} = -26.0088345946407$$
$$x_{16} = -81.8800849362763$$
$$x_{17} = -43.7836212073154$$
$$x_{18} = -1.73941330254706$$
$$x_{19} = 53.8801600148517$$
$$x_{20} = 9.89786286459462$$
$$x_{21} = -93.3716862417715$$
$$x_{22} = -17.9734625556164$$
$$x_{23} = 100.332288971932$$
$$x_{24} = 26.0088345946407$$
$$x_{25} = -27.8012489784829$$
$$x_{26} = 32.2920199018203$$
$$x_{27} = -29.6765132333509$$
$$x_{28} = 86.2251809979671$$
$$x_{29} = 50.066806514495$$
$$x_{30} = -88.8406876664365$$
$$x_{31} = -271.053061574645$$
$$x_{32} = -11.6902772484368$$
$$x_{33} = 68.2389450130531$$
$$x_{34} = -68.2389450130531$$
$$x_{35} = -188.694235158329$$
$$x_{36} = -50.066806514495$$
$$x_{37} = -75.5968996290967$$
$$x_{38} = 52.0048957599838$$
$$x_{39} = 94.0491036647521$$
$$x_{40} = 42.24288384771$$
$$x_{41} = 31.2172505929563$$
$$x_{42} = 6.48186125012126$$
$$x_{43} = -31.6146024788396$$
$$x_{44} = 56.3499918216746$$
$$x_{45} = -38.5752052089998$$
$$x_{46} = 75.5968996290967$$
$$x_{47} = 60.1633453220313$$
$$x_{48} = 40.3676195928421$$
$$x_{49} = -34.0844342856625$$
$$x_{50} = -125.862382086533$$
$$x_{51} = 68.9163624360338$$
$$x_{52} = -37.8977877860192$$
$$x_{53} = 19.0482318644804$$
$$x_{54} = -8.02259860972665$$
$$x_{55} = 26.8721545312654$$
$$x_{56} = 12.3676946714175$$
$$x_{57} = -31.2172505929563$$
$$x_{58} = -94.4464555506355$$
$$x_{59} = 76.2743170520774$$
$$x_{60} = -6.08450936423792$$
$$x_{61} = -73.658810383608$$
$$x_{62} = 61.9557597058735$$
$$x_{63} = 50.4641584003784$$
$$x_{64} = 88.8406876664365$$
$$x_{65} = 81.8800849362763$$
$$x_{66} = -61.9557597058735$$
$$x_{67} = 69.9911317448978$$
$$x_{68} = 6.08450936423792$$
$$x_{69} = 24.256647862796$$
$$x_{70} = 97.8624571651088$$
$$x_{71} = 8.02259860972665$$
$$x_{72} = -78.0667314359196$$
$$x_{73} = 79.9419956907876$$
$$x_{74} = -52.0048957599838$$
$$x_{75} = 63.0305290147375$$
$$x_{76} = 58.2880810671633$$
$$x_{77} = 44.1809730931988$$
$$x_{78} = -43.1062037843348$$
$$x_{79} = -94.0491036647521$$
$$x_{80} = -71.78354612874$$
$$x_{81} = 35.9596985405305$$
$$x_{82} = 16.1810481717742$$
$$x_{83} = 84.3499167430992$$
$$x_{84} = -6.48186125012126$$
$$x_{85} = 14.3057839169062$$
$$x_{86} = -19.7256492874611$$
$$x_{87} = 95.9871929102409$$
$$x_{88} = 94.4464555506355$$
$$x_{89} = -35.9596985405305$$
$$x_{90} = -45.7217104528042$$
$$x_{91} = 88.1632702434559$$
$$x_{92} = -63.7079464377182$$
Intervalos de convexidad y concavidad:Hallemos los intervales donde la función es convexa o cóncava, para eso veamos cómo se comporta la función en los puntos de flexiones:
No tiene corvaduras en todo el eje numérico