Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$\tan{\left(4 x \right)} + 4 = 0$$
Solve this equationThe points of intersection with the axis X:
Analytical solution$$x_{1} = - \frac{\operatorname{atan}{\left(4 \right)}}{4}$$
Numerical solution$$x_{1} = 67.998185799661$$
$$x_{2} = -50.5969368733537$$
$$x_{3} = 52.290222531712$$
$$x_{4} = -53.7385295269435$$
$$x_{5} = -60.8071129975205$$
$$x_{6} = 46.0070372245324$$
$$x_{7} = 34.2260647735707$$
$$x_{8} = -31.7473809518149$$
$$x_{9} = 16.1619070154294$$
$$x_{10} = 38.153055590558$$
$$x_{11} = 23.2304904860064$$
$$x_{12} = 40.5092500807503$$
$$x_{13} = -9.75623237668639$$
$$x_{14} = 96.2725196819691$$
$$x_{15} = 44.4362408977375$$
$$x_{16} = 12.2349161984422$$
$$x_{17} = -18.3956121740583$$
$$x_{18} = -75.729678102072$$