Hallemos los puntos de flexiones, para eso hay que resolver la ecuación
$$\frac{d^{2}}{d t^{2}} f{\left(t \right)} = 0$$
(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:
$$\frac{d^{2}}{d t^{2}} f{\left(t \right)} = $$
segunda derivada$$3 \left(- \frac{20 \sin{\left(2 t \right)}}{13} + \frac{22 \cos{\left(2 t \right)}}{13} - 3 e^{- 3 t}\right) = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$t_{1} = 52.2527694175688$$
$$t_{2} = 89.9518812606463$$
$$t_{3} = 39.6863988032096$$
$$t_{4} = 23.9784355352607$$
$$t_{5} = 44.3987877835943$$
$$t_{6} = 1.98896737543917$$
$$t_{7} = 6.69967593929243$$
$$t_{8} = 66.3899363587229$$
$$t_{9} = 93.0934739142361$$
$$t_{10} = 83.6686959534667$$
$$t_{11} = 38.1156024764147$$
$$t_{12} = 50.6819730907739$$
$$t_{13} = 45.9695841103892$$
$$t_{14} = 97.8058628946208$$
$$t_{15} = 88.3810849338514$$
$$t_{16} = 36.5448061496198$$
$$t_{17} = 71.1023253391076$$
$$t_{18} = 61.6775473783382$$
$$t_{19} = 30.2616208424403$$
$$t_{20} = 17.6952502280811$$
$$t_{21} = 67.9607326855178$$
$$t_{22} = 82.0978996266718$$
$$t_{23} = 3.55806811431214$$
$$t_{24} = 94.664270241031$$
$$t_{25} = 72.6731216659025$$
$$t_{26} = 25.5492318620556$$
$$t_{27} = 69.5315290123127$$
$$t_{28} = 28.6908245156454$$
$$t_{29} = 74.2439179926974$$
$$t_{30} = 14.5536575744913$$
$$t_{31} = 60.1067510515433$$
$$t_{32} = 22.4076392084658$$
$$t_{33} = 91.5226775874412$$
$$t_{34} = 16.1244539012862$$
$$t_{35} = 47.5403804371841$$
$$t_{36} = 31.8324171692351$$
$$t_{37} = 9.8412685941065$$
$$t_{38} = 58.5359547247484$$
$$t_{39} = 80.5271032998769$$
$$t_{40} = 75.8147143194923$$
$$t_{41} = 8.2704722673227$$
$$t_{42} = 96.2350665678259$$
$$t_{43} = 53.8235657443637$$
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:
Cóncava en los intervalos
$$\left[96.2350665678259, \infty\right)$$
Convexa en los intervalos
$$\left(-\infty, 1.98896737543917\right]$$