El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\left(\left(\left(\left(- \frac{4}{\pi} \cos{\left(x \right)} + \frac{\pi}{2}\right) - \frac{4}{\pi} \cos{\left(3 x \right)}\right) - \frac{4}{\pi} \cos{\left(5 x \right)}\right) - \frac{4}{\pi} \cos{\left(7 x \right)}\right) - \frac{4}{\pi} \cos{\left(9 x \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución numérica$$x_{1} = -43.7334519482469$$
$$x_{2} = -93.9989344056836$$
$$x_{3} = -37.9479570450877$$
$$x_{4} = 75.1493784841448$$
$$x_{5} = 6.0343401051694$$
$$x_{6} = -50.0166372554265$$
$$x_{7} = 68.8661931769653$$
$$x_{8} = -6.0343401051694$$
$$x_{9} = -81.9302541953448$$
$$x_{10} = 44.2311423522673$$
$$x_{11} = 119.131675634402$$
$$x_{12} = 25.3815864307285$$
$$x_{13} = 50.0166372554265$$
$$x_{14} = 100.282119712863$$
$$x_{15} = 88.2134395025244$$
$$x_{16} = -63.080698273806$$
$$x_{17} = 93.9989344056836$$
$$x_{18} = 37.9479570450877$$
$$x_{19} = 56.2998225626061$$
$$x_{20} = 0.248845202010187$$
$$x_{21} = -87.715749098504$$