Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$\frac{\tan{\left(x \right)}}{4} - 1 = 0$$
Solve this equationThe points of intersection with the axis X:
Analytical solution$$x_{1} = \operatorname{atan}{\left(4 \right)}$$
Numerical solution$$x_{1} = 86.1488193105924$$
$$x_{2} = 10.7505956244374$$
$$x_{3} = 20.1753735852068$$
$$x_{4} = -67.7892207153074$$
$$x_{5} = 57.8744854282843$$
$$x_{6} = 42.1665221603353$$
$$x_{7} = 35.8833368531558$$
$$x_{8} = 64.1576707354639$$
$$x_{9} = -74.072406022487$$
$$x_{10} = -8.09896029710135$$
$$x_{11} = -36.3732941794095$$
$$x_{12} = 95.5735972713618$$
$$x_{13} = -271.992743198644$$
$$x_{14} = 13.8921882780272$$
$$x_{15} = -152.612222362232$$
$$x_{16} = 92.432004617772$$
$$x_{17} = -23.8069235650503$$
$$x_{18} = -1.81577498992176$$
$$x_{19} = -45.7980721401789$$
$$x_{20} = -39.5148868329993$$
$$x_{21} = -96.0635545976156$$
$$x_{22} = -52.0812574473585$$
$$x_{23} = -89.780369290436$$
$$x_{24} = 7.60900297084762$$
$$x_{25} = -30.0901088722299$$